Quantum Science and Technology Seminar Series

(Formerly Quantum Information Science)

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Seminars will be held on Wednesdays, 3:00PM - 4:00PM, unless otherwise specified.

Current and Upcoming IQST Seminars

Wednesday 29th April, 2026 3:00 - 4:00pm in ES 136
Mohsen Bagherimehrab [University of Toronto]
Title: TBA
Abstract: TBA

Abstract:
TBA

Past IQST Seminars

2025

Quantum algorithms for non-linear differential equations
Arundhati Dasgupta [University of Lethbridge]
7 November 2025 - abstract -

Abstract:
We discuss new algorithms for solving non-linear differential equations for quantum computers. These include the non-linear pendulum, the Lorenz system which describe complex systems. We examine how the NISQ can still work with these systems which are sensitive to initial conditions.
Harnessing Rydberg Dynamics for Quantum Kernel Learning
Victor Drouin-Touchette [University of Sherbrooke]
1 October 2025 - abstract -

Abstract:
Neutral atoms in optical tweezers provide a scalable platform for quantum information processing, with strong interactions enabled by the Rydberg blockade. This talk explores how the resulting dynamics can be harnessed for practical quantum machine learning (QML), focusing on quantum kernel methods (QKMs). While QKMs often suffer from exponential concentration—requiring exponentially many measurements to resolve nontrivial kernels—we propose a novel kernel that avoids this pitfall by exploiting weak ergodicity-breaking in many-body Rydberg dynamics. We present analytical insights from a toy model, extensive simulations on synthetic data, and empirical results on real datasets. Crucially, the proposed kernel is both classically hard to simulate and implementable on current neutral atom quantum processors.
Quantum control of interlayer excitons in atomically thin semiconductor heterostructures
Nadine Leisgang [Harvard University]
28 July 2025 - abstract -

Abstract:
Two-dimensional materials and their heterostructures provide a highly tunable platform for many-body interactions and strongly correlated phenomena, including Mott insulators, generalized Wigner crystals and excitonic insulators. Of particular interest are atomically thin transition metal dichalcogenides (TMDs), such as MoS₂, MoSe₂ and WSe₂. They strongly interact with light to form excitons – electrons and holes bound by Coulomb attraction – which remain stable up to room temperature. The reduced dimensionality together with the relatively large effective mass and low kinetic energy of the charge carriers yield strong interactions between the individual electrons and excitons in the system. In addition, new excitonic species can be formed when combining two or more TMD monolayers, where the electrons and holes are separated between the individual layers – so-called interlayer excitons (IXs). The ability to engineer and control the properties of the thin semiconductors by external means makes these systems a versatile platform for rich exciton and electron physics and unique opto-electronic applications.

Here, we investigate strongly correlated phenomena in two varieties of TMD bilayers – homobilayer MoS₂ [1–3] and heterobilayer MoSe₂/WSe₂ [4–5]. These host IXs with large out-of-plane electric dipoles. We study the quantum-confined Stark effect of the IXs in these systems, as well as their interaction with additional charges.
On the Entropic Cost of Measuring to Infer
Nathan Shettell [National University of Singapore]
11 July 2025 - abstract -

Abstract:
Statistical inference involves measuring multiple systems parameterized by a common unknown parameter, with the aim of reducing uncertainty about that parameter. It is well-established that information processing, such as measurement and erasure, incurs an entropic cost. In this work, we quantify the minimal entropy required to perform inference under general measurement processes, focusing on how correlations between measurements affect this cost. We derive fundamental bounds in two paradigms: one where measurements are performed simultaneously, and another where they are performed sequentially; capturing the roles of spatial and temporal correlations, respectively. In both settings, we show that inter-measurement correlations can act as an entropy reservoir, allowing part of the entropy budget to be effectively recycled when correlations are leveraged. This recycled entropy can be used to perform additional measurements without increasing the overall entropic cost, thereby improving the quality of statistical inference. While developed in the context of inference, our framework applies more broadly, offering a thermodynamic lens on correlated measurement protocols in quantum information.
Waveguide-QED and entangled photon generation from a quantum dot in a waveguide
Tarun Patel [University of Waterloo]
23 April 2025 - abstract -

Abstract:
A two-level quantum system coupled to a one-dimensional electromagnetic mode has been a long-sought-after goal in quantum electrodynamics for the realization of the so-called “One-dimensional atom.” Such a system would enable the realization of key components for quantum networks, such as single or entangled photon sources, photon-photon gates, and spin-photon entanglement.
An InAsP quantum dot placed on the axis of a InP nanowire waveguide is an ideal system to achieve this goal. In this talk, I will present recent work done in collaboration with NRC-Canada to systematically investigate and improve the performance of such a nanowire quantum dot (NWQD) system. The first half of the presentation will focus on implementing near-unity in- and out-coupling of light from the nanowire waveguide into an optical fiber. This allows us to extend the waveguide mode from a 4K cryostat system to the outside world. Using this system, we perform Rayleigh scattering from the quantum dot without requiring any additional filtering technique for the first time, demonstrating a robust realization of a “One-dimensional atom.”
In the second half, I will present the use of the NWQD system as an entangled photon pair source and recent improvements obtained in source efficiency by implementing a bottom gold mirror using a ‘pick-and-place’ technique in a FIB-SEM system.
Dream Photonics - bringing light to semiconductor chips
Matthew Mitchell [Dream Photonics]
5 March 2025 - abstract -

Abstract:
Dream Photonics is a semiconductor IP company focused on providing Silicon Photonics and Electronics IP and assembly solutions. Dream offers the industry’s most diverse portfolio of multi-foundry IP building blocks that foundries and end-customers license and integrate into their chip. Dream offers the industry’s most prolific assembly solutions, enabling customers to hybrid integrate lasers, optical amplifiers, fibers, and other optical components, from prototyping to high-volume manufacturing. Dream Photonics is located in Vancouver BC and Woodinville WA.

In this seminar I will provide an overview of the services we offer, with a focus on optical packaging and low-loss optical coupling: I will review current methods of optical I/O that are used in industry, and present the approach we are taking at Dream Photonics to help our customers solve their problems from the data communications space to quantum hard problems. Our approach utilizes two-photon lithography to 3D print polymer micro-optics such as photonic wire bonds, and facet-attached microlenses directly on photonic chips, and III-V lasers, enabling flexible, hybrid-integration of disparate material platforms, and photonic devices. This technique enables printing of custom optics for each application/component with 100 nm placement accuracy and ~ 1 μm printing resolution. I will present this technology, and our recent results on demonstrating facet-attached microlenses for fiber-to-chip coupling with multiple silicon photonic foundries with broadband, < 1.5 dB insertion loss, and our envisioned path to the
Efficient Hamiltonian Simulation: A Utility Scale Perspective for Covalent Inhibitor Reactivity Prediction (CMS Seminar)
Dmitri Iouchtchenko [Haiqu]
27 February 2025 - abstract -

Abstract:
Quantum computing applications in the noisy intermediate-scale quantum (NISQ) era demand algorithms capable of generating shallower circuits that are feasible to run on today's quantum systems. This is a challenge, particularly for quantum chemistry applications, considering the inherent complexity of molecular systems. In this work, we demonstrate advancements that expand the size of chemistry problems that can be run on today’s quantum systems by applying hardware-efficient approaches, such as Quantum-Centric Data-Driven Research and Development (QDDRD), optimized algorithms with reduced circuit depth, and execute the experiments with middleware-supported quantum error mitigation. We report up to a 29-fold reduction in circuit depth for covalent drug molecules, enabling Hamiltonian dynamics for reactivity predictions, assuming all-to-all connectivity of quantum hardware. When employed on IBMQ’s Heron architecture, we see up to a 16-fold reduction. The overarching impact of this work is that it highlights promising methods that allow researchers to explore the dynamics of commercially relevant chemistry on real quantum hardware via Hamiltonian simulation.
A simple truth hidden in plain sight: All molecules are entangled according to chemical common sense
Jing Kong [Middle Tennessee State University]
4 February 2025 - abstract -

Abstract:
In this talk, I show that a simple but nontrivial equation exists for molecules and how the equation changes the perception of a molecule in light of quantum entanglement. Physical objects have been shown to entangle quantum-mechanically over visible distances, which challenges the classic view that separated objects are independent of each other. I argue that chemical common sense actually supports the entanglement view. Specifically, chemical common sense can be summarized as a simple, nontrivial equation showing that all molecules are entangled in the number of electrons. Wavefunction interpretation of this equation of nature shows that all molecules in the physical world are always entangled, albeit not always locally real. Furthermore, it leads to the possibility of the number of electrons of a molecule being fractional. The continuity of the number of electrons allows the definition of the chemical potential for the electrons in a single molecule, which has nothing to do with temperature. The quantum entanglement can be viewed as saying that all molecules share the same chemical potential. An equation equivalent to the new question can be formulated with a state function using the chemical potential as a variable that exhibits an asymptotic additivity. Discussions are mostly conceptual.
Towards quantum interconnects: entangling microwave and optical photonic qubits
David Lake [California Institute of Technology]
9 January 2025 - abstract -

Abstract:
Modern computing and communication technologies such as supercomputers and the internet are based on optically linked networks of information processors operating at microwave frequencies. An analogous architecture has been proposed for quantum networks, using optical photons to distribute entanglement between remote superconducting quantum processors. Here I will discuss progress towards such a network, discussing our recent demonstration of a chip-scale source of entangled optical and microwave photonic qubits. Our device platform integrates a piezo-optomechanical transducer with a superconducting resonator which is robust under optical illumination. We drive a photon-pair generation process and employ a dual-rail encoding to prepare entangled states of microwave and optical photons. This entanglement source can directly interface telecom wavelength time-bin qubits and GHz frequency superconducting qubits, two well-established platforms for quantum communication and computation, respectively.

2024

Towards higher-order quantum mechanics (Eric Milner's Graduate Scholarship Lecture)
Eric Milner [University of Calgary]
27 November 2024 - abstract -

Abstract:
The axioms of quantum mechanics provide a mathematical framework for defining quantum systems, states, and operations. These definitions are consistent in that quantum operations map quantum states to other quantum states. Interestingly, an agent can manipulate a quantum operation and transform it into another quantum operation. Therefore, we can define quantum super-operations as maps from quantum operations to quantum operations. We refer to quantum operations as first-order operations, and super-operations as second-order operations. Similarly, we can recursively define operations of order n as maps from operations of order n-1 to operations of order n-1.

In this talk, I will introduce quantum mechanics and the mathematical framework used to describe quantum systems, states, and operations. Then, I will present how type theory aids in investigating higher-order quantum operations and their properties.
Introducing the Ramaniton: The quasiparticle for Raman scattering
Rogério de Sousa [University of Victoria]
19 November 2024 - abstract -

Abstract:
In Raman scatering, pump photons that are incident on a material are
able to emit or absorb materials' excitations such as phonons and
orbital transitions. This process generates red-shifted (Stokes) and blue-shifted (antiStokes) photons that are usually uncorrelated with
each other. When real or virtual excitations emitted by a Stokes photon are coherently absorbed by another pump photon, an entangled Stokes-antiStokes photon pair is created, in a process analogous to the formation of Cooper pairs in superconductors [1].

In this talk we will show that this mechanism provides the microscopic
underpinning for the phenomena of four-wave mixing in quantum
optics, one of the main methods to generate squeezed states of light that are key to
proposals of quantum computing, sensing, and communication with photons.

We will argue that it's fruitful to take a "condensed matter physics approach" and
treat Raman-interacting photons and phonons as a hybrid excitation,
the Ramaniton quasiparticle [2].

The Ramaniton enables nonperturbative theories for the
evolution of photons in waveguides formed by group IV semiconductors
such as silicon and diamond, enabling the design of photonic devices
that exploit optical phonons for optimal generation of two-mode squeezed states of light.

[1] A. Saraiva, F.S.D.A. Júnior, R. De Melo E Souza, A.P. Pena,
C.H. Monken, M.F. Santos, B. Koiller, and A. Jorio, Photonic
Counterparts of Cooper Pairs, Phys. Rev. Lett. 119, 193603 (2017).

[2] S. Timsina, T. Hammadia, S.G. Milani, F.S.D.A. Júnior, A. Brolo,
and R. de Sousa, Resonant squeezed light from photonic Cooper pairs, Phys. Rev. Res. 6, 033067 (2024).
The good, the bad, and the ugly in quantum computing: Computational power, intrinsic noise, and transient faults
Paolo Rech [University of Trento]
31 October 2024 - abstract -

Abstract:
Quantum computing is a new computational paradigm, expected to revolutionize the computing field in the next few years.
Qubits, the atomic units of a quantum circuit, exploit the quantum physics properties to increase the parallelism and speed of computation.
Unfortunately, qubits are both intrinsically noisy and highly susceptible to external sources of faults, such as ionizing radiation.
The reported qubits error rate is so high that researchers are questioning the large-scale adoption of quantum computers and forces unpractical mitigation solutions such as installing the quantum computer in underground caves.
Innovative solutions to improve the reliability of quantum applications are then highly necessary.
In the talk, after providing all information and background needed to understand quantum computing basics and an overview of the available quantum technologies vulnerabilities, we will present the available hardening solutions and the open challenges that need to be addressed. We will consider both the intrinsic noise, that has a predictable and incremental effect, and radiation-induced transient faults, that are stochastic and modify the qubit in an unpredictable way. Based on the latest studies and radiation experiments performed on real quantum machines, we will show how to model the transient faults in a qubit and how to inject this fault in a quantum circuit to track its propagation. We will discuss the vulnerability of qubits and of circuits, identifying the most critical parts and the main course for output corruption. Finally, we will provide an overview of the open (reliability) challenges in quantum computing to stimulate further studies and solutions.
Fungi under the magnet: A novel magnetic field platform and discoveries in yeast magnetobiology
Daniel Charlebois [University of Alberta]
29 August 2024 - abstract -

Abstract:
Electromagnetic fields are known to affect living matter. However, the magnetobiology of microorganisms largely remains to be elucidated, especially for fungi. To address this knowledge gap, we used AutoCAD, COMSOL Multiphysics, and 3D printing to develop a device to expose microbial populations to static magnetic fields. We found that magnetic fields can slow the spatially structured expansion of biofilm-like budding yeast (Saccharomyces cerevisiae) on semi-solid media. We also found that magnetic fields do not affect the growth of yeast cells in well-mixed liquid media. This research is innovating adaptable, open-source devices to perform electromagnetic experiments on microbes and is advancing our understanding of the effects of electromagnetic fields on fungi.
Harnessing utility for quantum advantage
Alexandre Choquette [IBM Quantum]
7 August 2024 - abstract -

Abstract:
With a multitude of quantum demonstrations on 100+ qubits, quantum computing is now firmly in the era of utility where quantum computers can serve as a scientific tool to explore a new scale of problems that classical methods may not be able to solve. This scale, combined with advances in algorithms, is fundamental to enabling quantum advantage; the point where quantum computers can faithfully run one or more tasks providing scientific or business value with more accuracy, efficiently, or cost-effectiveness than with classical computation alone. In this talk, I will present some of the latest hardware and algorithmic developments at IBM Quantum that are making our technology roadmap a reality. I will also explain how the scientific community of the University of Calgary can start programming on an IBM Quantum system today.
Multi-armed stochastic bandits and their applications to quantum information
Josep Lumbreras Zarapico [Centre for Quantum Technologies Singapore]
4 July 2024 - abstract -

Abstract:
In this talk, I'll address the exploration-exploitation dilemma in reinforcement learning, focusing on its formalization in multi-armed stochastic bandits (MAB). I'll discuss key techniques like optimism in the face of uncertainty, exemplified by algorithms such as upper confidence bounds (UCB) and LinUCB. Transitioning to quantum tasks, I'll apply the MAB framework for learning quantum state properties, online/adaptive quantum state tomography, and developing recommender systems for quantum data.
Laser-fabricated quantum photonic sensors in diamond
Shane Eaton [IFN-CNR and Department of Physics at Politecnico di Milano]
28 June 2024 - abstract -

Abstract:
The negatively charged nitrogen-vacancy (NV) center is a defect in diamond which is capable of high sensitivity, high resolution sensing of electromagnetic fields. An integrated optics platform in diamond is beneficial for quantum-enabled sensing, due to increased stability, enhanced optical interaction with NVs and novel 3D configurations.
We characterize the properties of NVs and photonics formed by focused femtosecond laser pulses in synthetic high pressure high temperature and chemical vapor deposition diamond. We present quantum sensors based on integrated photonics in diamond, with magnetic field sensitivities on the order of nT Hz^-0.5.
Hunting for quantum butterflies
Shohini Ghose [Wilfrid Laurier University and Quantum Algorithms Institute]
16 January 2024 - abstract -

Abstract:
Unpredictability manifests itself in very different ways at the classical and the quantum level. This has led to long-standing open questions, including the connection between chaos theory and quantum mechanics. Recent advances in quantum computing have made it possible to study foundational questions about the quantum-classical boundary in an experimental setting. This talk will discuss the first quantum simulations of chaos on a programmable quantum computer, and the identification of new quantum resonances in periodic systems that have no classical analog.

*** The book signing will start after the talk from 3:30pm****

2023

TBA
Jacob Barnett [Perimeter Institute for Theoretical Physics]
21 November 2023 - abstract -

Abstract:
TBA
Entanglement of nanophotonic quantum memory nodes via a telecommunication network
Can Knaut [Harvard University]
20 November 2023 - abstract -

Abstract:
A key challenge in realizing practical quantum networks for long-distance quantum communication involves robust entanglement between quantum memory nodes connected via fiber optical infrastructure. Here, we demonstrate a two-node quantum network composed of two-qubit registers based on silicon-vacancy (SiV) centers in nanophotonic diamond cavities integrated with a telecommunication fiber network. Remote entanglement is generated via the cavity-enhanced interactions between the SiV's electron spin qubits and optical photons. Long-lived nuclear spin qubits are used for integrated error detection and a second-long entanglement storage. By integrating efficient bi-directional quantum frequency conversion of photonic communication qubits to telecommunication frequencies (1350 nm), we demonstrate entanglement of two nuclear spin memories through 40 km spools of low-loss fiber and a 35 km long fiber loop deployed in the Boston area urban environment, representing an enabling step towards practical quantum repeaters and large-scale quantum networks.
Multifunctional scanning microscopy with quantum spins in diamond
William Huxter [ETH Zurich]
14 November 2023 - abstract -

Abstract:
Quantum sensing based on nitrogen vacancy (NV) centers in diamond is an established technique for imaging nanoscale magnetic materials. Magnetic fields are sensed by measuring the spin resonance of a single NV center at the apex of a scanning probe. Here, I will present recent developments in improving and expanding the scanning NV toolbox. This includes a detection scheme based on AC dynamical decoupling that extends the coherence time and improves sensitivity. This detection scheme enabled visualization of non-diffusive current flow in graphene. A variant of this detection method, based on DC-to-AC conversion, was used to image weak static fields, including those generated by antiferromagnetic atomic steps. Additionally, for the first time, we could image electric fields from ferroelectric materials and visualize their domain patterns. These demonstrations expand the scope of nanoscale phenomena accessible to scanning NV microscopy.
What happens to entropy production when conserved quantities fail to commute with each other
Billy Braasch [National Institute of Standards and Technology]
25 October 2023 - abstract -

Abstract:
A fundamental challenge is to define quantum thermodynamic
quantities-for example, heat, work, and entropy production. We extend the definition of entropy production to a deeply quantum regime involving noncommuting observables. Consider two systems prepared in different thermal states. A unitary transports observables ("charges") between the systems. Three common formulae model the entropy produced. They cast entropy as an extensive thermodynamic variable, as an informationtheoretic uncertainty measure, and as a quantifier of irreversibility. Often, the charges are assumed to commute with each other (e.g., energy and particle number), and the entropy-production formulae equal each other. Yet quantum charges can fail to commute, inviting generalizations of the
three formulae. Charges’ noncommutation, we find, breaks the formulae's
equivalence. Furthermore, different formulae quantify different physical
effects of charges' noncommutation on entropy production. For instance,
entropy production can signal contextuality-true nonclassicality-by
becoming nonreal. This work opens the door of stochastic
thermodynamics to charges that are peculiarly quantum by failing to
commute with each other.
Breakthrough in enhancement of holes characteristics in strained germanium on silicon leading to new opportunities in practical quantum computing and classical cold electronics
Sergei Studenikin [National Research Council of Canada]
12 October 2023 - abstract -

Abstract:
In this presentation I will talk about the compressively strained germanium on silicon material platform for quantum as well for classical electronics.
Space quantum key distribution
Paul J. Godin [University of Waterloo]
11 October 2023 - abstract -

Abstract:
This talk will present an overview of the upcoming Canadian Quantum Encryption and Science Satellite (QEYSSat) mission, including payload and ground station development. QEYSSat's primary mission goal is to preform quantum key distribution (QKD) using polarization-based protocols such as BB84. To achieve this, QEYSSat is equipped with a photon detector module that will record polarization encoded photons from the ground.
Additionally, a quantum optical ground station (QOGS) is under development at the University of Waterloo; this process includes the characterization of light pollution at the chosen location, construction of a custom telescope capable of sending/receiving signals with QEYSSat, and the development of different quantum sources. The current sources being investigated are an entangled photon source and a weak coherent pulse source (WCP).
Lastly, QEYSSat also will have a WCP source on board to send polarization encoded photons from space to ground. This secondary payload is being developed and tested at the University of Waterloo; while the photons sent from this payload will be detected and analyzed by a University of Calgary ground station.
Multiphoton and side-channel attacks in mistrustful quantum cryptography
Damián Pitalúa-García [University of Cambridge]
28 September 2023 - abstract -

Abstract:
Mistrustful cryptography includes important tasks like bit commitment, oblivious transfer, coin flipping, secure computations, position authentication, digital signatures and secure unforgeable tokens. Practical quantum implementations presently use photonic setups. In many such implementations, Alice sends photon pulses encoding quantum states and Bob chooses measurements on these states. In practice, Bob generally uses single-photon threshold detectors, which cannot distinguish the number of photons in detected pulses. Also, losses and other imperfections require Bob to report the detected pulses. Thus, malicious Alice can send and track multiphoton pulses and thereby gain information about Bob\\\'s measurement choices, violating the protocols\\\' security. Here, we provide a theoretical framework for analyzing such multiphoton attacks, and present known and new attacks. We illustrate the power of these attacks with an experiment, and study their application to earlier experimental demonstrations of mistrustful quantum cryptography. We analyze countermeasures based on selective reporting and prove them inadequate. We also discuss side-channel attacks where Alice controls further degrees of freedom or sends other physical systems.
Based on Mathieu Bozzio, Adrien Cavaillès, Eleni Diamanti, Adrian Kent, and Damiàn Pitalúa-García, PRX Quantum 2, 030338 (2021). https://doi.org/10.1103/PRXQuantum.2.030338
A routing algorithm for surface code compilation
Yvual Sanders [University of Technology Sydney]
25 September 2023 - abstract -

Abstract:
The leading contender for fault-tolerant quantum computing is based upon a topological quantum error-correcting code called the "surface code". A recent paper from Litinski [doi:10/ggz5v3] articulates the basic operations of the surface code in terms of manipulating a grid of surface code "patches". In this talk I describe an algorithm for translating a quantum circuit into a sequence of Litinski-style manipulation of surface code patches. Our algorithm would play a crucial role in the compilation of quantum algorithms for surface code quantum computers.
Institutional presentation of CNRS
Jan Matas [CNRS]
14 September 2023 - abstract -

Abstract:
Institutional presentation of CNRS
Employing coaxmon-based qudits for quantum information processing
Shuxiang Cao [University of Oxford]
21 August 2023 - abstract -

Abstract:

Superconducting circuits have emerged as a promising platform for quantum information processing. However, scalability remains a challenge, and one of the difficulties is the complexities of packaging and wiring large qubit arrays. To address this, "coaxmon", a variant of transmon qubits, was developed. It offers an off-chip wiring solution while maintaining high coherence [1]. This presentation reports the recent progress in coaxmon design and our efforts in employing coaxmons as qudits, utilizing more than two levels of a transmon for quantum computation. We share our research on qutrit and qudit gate benchmarking analyses using Gate-Set Tomography [2,3]. Additionally, we demonstrate a qutrit quantum classifier for quantum machine learning with the coaxmon qudit. We have also utilized four transmon levels to emulate a two-qubit system and demonstrate a variational quantum eigensolver algorithm on this emulator [3]. We analyze the noise affecting the quantum algorithm and report the strategies we have adopted for error mitigation.

[1] P. A. Spring et al., High coherence and low cross-talk in a tileable 3D integrated superconducting circuit architecture, Science Advances, vol. 8, no. 16. American Association for the Advancement of Science (AAAS), Apr. 22, 2022.

[2] S. Cao et al., "Efficient qutrit gate-set tomography on a transmon." arXiv, 2022.

[3] S. Cao et al., "Emulating two qubits with a four-level transmon qudit for variational quantum algorithms." arXiv, 2023.
Quantum dynamics in noisy systems: from control to chaos
Aurélia Chenu [University of Luxembourg]
2 August 2023 - abstract -

Abstract:
Quantum experiments are performed in noisy platforms. In NISQ devices, realistic setups can be described by open systems or noisy Hamiltonians. Starting from a generic noisy Hamiltonian, I will first present a scheme to simulate long-range and many-body interactions in a quantum platform [1]. We then engineer a protocol for the fast thermalization of a harmonic oscillator [2], which can be adapted to generate squeezed thermal states [3] in arbitrary time.

Then, going beyond the noise-averaged density matrix, I will introduce the concept of stochastic operator variance (SOV) of an observable. The SOV [4] is an operator that characterizes the deviation of any operator from the noise-averaged operator in a stochastic evolution governed by the Hamiltonian. As such, it is relevant in the quantum simulation of open systems using NISQ devices, e.g., to engineer a given dissipative evolution. Surprisingly, we find that the evolution of the noise-averaged variance relates to an out-of-time-order correlator (OTOC), which connects fluctuations of the system with scrambling. This connection may allow computing the Lyapunov exponent and experimentally access OTOCs without the need to invert the sign of the Hamiltonian. I will illustrate the results in the stochastic LMG model, and show how noise changes the phase diagram of the system.

[1] A. Chenu, M. Beau, J. Cao, and A. del Campo, Quantum Simulation of Generic Many-Body Open System Dynamics Using Classical Noise. Phys. Rev. Lett. 118:140403 (2017).

[2] L. Dupays, I. L. Egusquiza, A. del Campo, and A. Chenu. Superadiabatic thermalization of a quantum oscillator by engineered dephasing, Phys. Rev. Res. 2:033178 (2020).

[3] L. Dupays and A. Chenu. Dynamical engineering of squeezed thermal state, Quantum 5:449 (2021).

[4] P. Martinez-Azcona, A.Kundu, A. del Campo, and A. Chenu, ArXiv:2302.12845 (2023).
Dynamics of a quantum phase transition in a quantum annealer
Adolfo Del Campo Echevarria [University of Luxembourg]
2 August 2023 - abstract -

Abstract:
The dynamics of a quantum phase transition is nonadiabatic and characterized by the formation of topological defects. The Kibble-Zurek mechanism (KZM) quantifies the breakdown of adiabaticity by predicting a universal law for the average defect density as a function of the rate at which the transition is crossed. Universal features beyond the KZM are found in the fluctuations of the defect number. We shall present these and other predictions beyond KZM and report their test in quantum annealing devices.
Entangled quantum cellular automata, physical complexity, and Goldilocks rules
Lincoln Carr [Colorado School of Mines]
4 July 2023 - abstract -

Abstract:

Cellular automata are interacting classical bits that display diverse emergent behaviors, from fractals to random-number generators to Turing-complete computation. We discover that quantum cellular automata (QCA) can exhibit complexity in the sense of the complexity science that describes biology, sociology, and economics. QCA exhibit complexity when evolving under 'Goldilocks rules' that we define by balancing activity and stasis. Our Goldilocks rules generate robust dynamical features (entangled breathers), network structure and dynamics consistent with complexity, and persistent entropy fluctuations. Present-day experimental platforms—Rydberg arrays, trapped ions, and superconducting qubits—can implement our Goldilocks protocols, making testable the link between complexity science and quantum computation exposed by our QCA.

The inability of classical computers to simulate large quantum systems is a hindrance to understanding the physics of QCA, but quantum computers offer an ideal simulation platform. If time allows, I will discuss our recent experimental realization of QCA on a digital quantum processor, simulating a one-dimensional Goldilocks rule on chains of up to 23 superconducting qubits. Employing low-overhead calibration and error mitigation techniques, we calculate population dynamics and complex network measures indicating the formation of small-world mutual information networks. Unlike random states, these networks decohere at fixed circuit depth independent of system size, the largest of which corresponds to 1,056 two-qubit gates. Such computations may open the door to the employment of QCA in applications like the simulation of strongly-correlated matter or beyond-classical computational demonstrations.

References:
1. LE Hillberry, MT Jones, DL Vargas, P Rall, N Yunger Halpern, N Bao, S Notarnicola, S Montangero, LD Carr, "Entangled quantum cellular automata, physical complexity, and Goldilocks rules," Quantum Science and Technology, v. 6, p. 045017 (2021)
2. EB Jones, LE Hillberry, MT Jones, M Fasihi, P Roushan, Z Jiang, A Ho, C Neill, E Ostby, P Graf, E Kapit, and LD Carr, "Small-world complex network generation on a digital quantum processor," Nature Communications v. 13, p. 4483 (2022)
3. LE Hillberry, M Fasihi, L Piroli, N Yunger Halpern, T Prosen, and LD Carr, "Thermodynamics, scrambling, chaos, and integrability in quantum cellular automata," in preparation (2023)
Efficient quantum simulation of partial differential equations
Nana Liu [Institute of Natural Sciences, University of Michigan-Shanghai Jiao Tong University]
25 April 2023 - abstract -

Abstract:
What kinds of scientific computing problems are suited to be solved on a quantum device with quantum advantage? It turns out that by transforming a partial differential equation (PDE) into a higher-dimensional space, certain important issues can be resolved while at the same time not incurring a curse of dimensionality, when tackled by a quantum algorithm.

I'll introduce a simple new way - called Schrodingerisation - that transforms any linear partial differential equation into a set of Schrodinger's equations. This allows one to simulate any general linear partial differential equation via quantum simulation.

Furthermore, Schrodingerisation can also be applied to quantum dynamics in the presence of artificial boundary condition. This method can also be applied to problems in linear algebra by transforming iterative methods in linear algebra into evolution of ordinary differential equations, like the Jacobi method and the power method. This allows us to directly use quantum simulation to solve the linear system of equations and find maximum eigenvectors and eigenvalues of a given matrix.

I'll also explore ways in which quantum algorithms can be used to efficiently solve not just linear PDEs but also certain classes of nonlinear PDEs, like nonlinear Hamilton-Jacobi equations and scalar hyperbolic equations, which are useful in many areas like optimal control and machine learning. PDEs with uncertainties can also be tackled more efficiently with quantum algorithms.
Quantum sensing and imaging with diamond spins
Ania Jayich [University of California, Santa Barbara]
30 March 2023 - abstract -

Abstract:
Solid state spin qubits, in particular the nitrogen vacancy (NV) center in diamond, offer a path towards truly
nanoscale imaging of condensed matter and biological systems with sensitivity to single nuclear spins.
Here I discuss our NV-based magnetic imaging experiments as applied to condensed matter systems,
where we have imaged current flow patterns in graphene in order to reveal the transition from ohmic to
electron-collision-dominated flow regimes. A grand challenge to improving the spatial resolution and
magnetic sensitivity of the NV is mitigating surface-induced quantum decoherence, which I will discuss in
the second part of this talk. Decoherence at interfaces is a universal problem that affects many quantum
technologies, but the microscopic origins are as yet unclear. Our studies guide the ongoing development
of quantum control and materials control, pushing towards the ultimate goal of NV-based single nuclear
spin imaging.
Quantum engagement and applications - Natural Resources Canada
Asif Iqbal [Natural Resources Canada]
9 March 2023 - abstract -

Abstract:
To respond to the growth of quantum technologies through national strategies and initiatives, the Government of Canada announced the development of a National Quantum Strategy in Budget 2021 to amplify Canada's significant strength in quantum research, guide the development of the country's quantum ecosystem and position Canada as a global leader in quantum technology space. Natural Resources Canada, along with other government agencies, are working with private companies, and academic institutes to pursue use cases on how to apply quantum technologies to real world issues. This presentation will provide a broader context for why the natural resource sectors are potential end-users of quantum technologies such as quantum sensors, quantum materials, quantum computation and communication. We will also briefly demonstrate some examples of how quantum technologies can be deployed in the natural resource sectors and support developments in clean technology and energy, sensing and imaging instruments. Discussions after the presentation will help us explore the potential for collaborating with the University of Calgary on quantum technologies to support Canada’s climate actions, net zero targets and energy transitions.
Quantum (Un)complexity: A resource for quantum computation
Anthony Christopher Munson [Joint Center for Quantum Information and Computer Science NIST and University of Maryland]
1 March 2023 - abstract -

Abstract:
Under random dynamics, a system's quantum complexity - which quantifies the difficulty of preparing a desired state from a simple, tensor-product state - increases linearly up to times exponential in the system's size, long after most physical observables have thermalized. The observation that complexity saturation is a late stage of quantum thermalization suggests that a state's lack of complexity, or "uncomplexity," is a useful resource for quantum computation: Much as a system far from thermal equilibrium can serve as a resource in information-processing tasks, a state with high uncomplexity, i.e., a low-complexity state such as |0^n> - can be utilized as "blank scrap paper" for quantum computers. It is natural, therefore, to view uncomplexity through the lens of a resource theory. In a resource theory, an agent can perform any operation subject to a fixed set of simple rules, and can identify which tasks are achievable under these rules and which tasks require additional resources. We define a resource theory of uncomplexity, and then construct protocols in the resource theory for extracting uncomplexity from a state and for expending uncomplexity to imitate a state. Moreover, we show that a new quantity, the complexity entropy, quantifies the efficiencies with which we can perform uncomplexity extraction and expenditure, and thereby quantifies the resource requirements for one-shot thermodynamic erasure (Landauer erasure) under computational limitations.

https://ucalgary.zoom.us/j/93598611120?pwd=QzFKNUc1RGJReVlIS2pJeXlOeG0vdz09

Meeting ID: 935 9861 1120
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Towards realization of protected qubits using topological superconductivity
Javad Shabani [New York University]
1 February 2023 - abstract -

Abstract:
A central goal in quantum computing research is to protect and control quantum information from noise. This talk will provide recent progress on the developing field of topological superconductivity where we can encode information in spatially separated Majorana zero modes (MZM). We show that topological superconductivity can be achieved in certain hybrid materials where the topological properties are not found in the constituent materials. These special MZMs are formed at the location of topological defects (e.g. boundaries, domain walls,..) and manifest non-Abelian braiding statistics that can be used in noise-free unitary gate operations. We show by engineering a reconfigurable domain walls on a Josephson junction we can create a scalable platform to study MZM properties and their applications in quantum information science.

2022

Toward a comprehensive view of the molecular bases of magnetoreception from realistic biological models
Aurélien de la Lande [Université Paris Saclay,CNRS]
1 December 2022 - abstract -

Abstract:
The molecular basis of magnetoreception continues to stimulate active research worldwide. The dominant models attribute the magnetic sense to coherent spin dynamics in radical pairs/triads within the flavo-protein cryptochrome. Our research groups have embarked on an ambitious theoretical program aiming at unravelling the molecular basis of magnetoreception, combining spin dynamics, accurate electronic structure calculations and molecular dynamics simulations of proteins.

In the first part of this seminar, we will summarize our results on radical pair production in cryptochrome proteins by cascades of photoinduced electron transfers. We will contrast various mechanisms leading to the formation of flavin and tryptophan radicals[1,2]. We will evidence the influence of nuclear quantum effects or other fine quantum effects.

In the second part we will lay the foundations of the assessment of an original triad of radical model. We will first illustrate the advantages of a triad radical mechanism within an actual avian cryptochrome protein[3]. We will report accurate hyperfine coupling tensors obtained by auxiliary density functional theory along classical molecular dynamics simulations[4]. Finally, we will report recent exciting findings about putative superoxide anions location sites that could, in the context of the triad model, both enhance the sensitivity of the compass and protect the protein against oxidative stress. Perspectives for future studies will be proposed.

References
[1] Cailliez F, Muller P, Firmino T, Pernot P and de la Lande A 2016 Energetics of Photoinduced Charge Migration within the Tryptophan Tetrad of an Animal (6-4) Photolyase J. Am. Chem. Soc. 138 1904-15
[2] Firmino T, Mangaud E, Cailliez F, Devolder A, Mendive-Tapia D, Gatti F, Meier C, Desouter-Lecomte M and de la Lande A 2016 Quantum effects in ultrafast electron transfers within cryptochromes Phys. Chem. Chem. Phys. 18 21442-57
[3] Deviers J, Cailliez F, de la Lande A and Kattnig D R 2022 Anisotropic magnetic field effects in the re-oxidation of cryptochrome in the presence of scavenger radicals J. Chem. Phys. 156 025101
[4] Deviers J, Cailliez F, Gutierrez B Z, Kattnig D R and de la Lande A 2022 Ab initio derivation of flavin hyperfine interactions for the protein magnetosensor cryptochrome Phys. Chem. Chem. Phys. 24 16784-98.
Few-body perspective on collective pairing between fermions
Tomasz Sowinski [Polish Academy of Science]
8 November 2022 - abstract -

Abstract:
In this perspective I will discuss recent concepts giving a route to a better understanding of conventional and unconventional pairing mechanisms between opposite-spin fermions arising in mesoscopic systems. With special attention, I will focus on detectability of correlations between particles. Finally, I will try to convince you that state-of-the-art experiments with few ultracold fermions may finally break an impasse and give pioneering and unquestionable verification of the existence of correlated pairs with non-zero center-of-mass momentum.

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Meeting ID: 921 2574 2812
Semiconductor Quantum Cavity QED Platforms: Bloch Exciton-Polaritons and Rydberg Excitons
Kim Na Young [University of Waterloo]
19 October 2022 - abstract -

Abstract:
Our aim to build solid-state quantum systems and especially we have been working on exciton-polariton quantum simulators, which we like to construct a designated Hamiltonian solver. Microcavity excition-polaritons are hybrid quantum quasi-particles as an admixture of cavity photons and quantum- well excitons. In order to search for novel phases resulting from the interplay of geometry, spin and interaction, we engineered two-dimensional (2D) honeycomb lattices where Bloch exciton-polaritons form artificial bandstructures and their properties are explained with the two-flavor Hamiltonians. And we recently study the scaling laws of Rydberg excitons at different temperatures, upon which we like to establish solid-state Rydberg quantum technologies.

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Uncertainty relations for Non-Hermitian systems
Namrata Shukla [Banaras Hindu University]
28 September 2022 - abstract -

Abstract:
Robertson's formalized version of the Heisenberg uncertainty relation contains a state of interest and two incompatible observables that are Hermitian operators. We construct uncertainty relation for PT-invariant non-Hermitian quantum systems by introducing a more general condition of "good observable". Our construction is not limited to the PT-symmetric phase but also valid in the PT-broken phase. In contrast to the usual quantum theory, a good observable can also be a non-Hermitian operator for such systems. We show that the non-Hermitian Hamiltonian itself qualifies as a good observable in the PT-symmetric phase, but not in the broken phase. Consequently, this fact can be used as a diagnostic tool to detect the PT phase transition in any arbitrary finite-dimensional system.ORobertson's formalized version of the Heisenberg uncertainty relation contains a state of interest and two incompatible observables that are Hermitian operators. We construct uncertainty relation for PT-invariant non-Hermitian quantum systems by introducing a more general condition of "good observable". Our construction is not limited to the PT-symmetric phase but also valid in the PT-broken phase. In contrast to the usual quantum theory, a good observable can also be a non-Hermitian operator for such systems. We show that the non-Hermitian Hamiltonian itself qualifies as a good observable in the PT-symmetric phase, but not in the broken phase. Consequently, this fact can be used as a diagnostic tool to detect the PT phase transition in any arbitrary finite-dimensional system.

IQST seminar by Namrata Shukla

Topic: Uncertainty relations for Non-Hermitian systems
Time: Sep 28, 2022 03:00 PM Edmonton

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A molecular optomechanics approach to Surface-Enhanced Raman Scattering
Javier Aizpurua [Center for Materials Physics in San Sebastián (CSIC-UPV/EHU)]
17 August 2022 - abstract -

Abstract:
Surface-Enhanced Raman Scattering (SERS) exploits the strong interaction between molecules and plasmonic resonances in metallic nanostructures enabling the characterization of vibrational modes of a very small amount of molecules. A classical description of SERS in plasmonic nanoantennas properly addresses the strong enhancement of the Raman lines in the emission spectrum, with the properties of molecular vibrations assumed to be fixed. A recently introduced quantum description of SERS, based on molecular optomechanics [1,2,3] shows how the width and frequency of the Raman lines can change for very intense laser powers, corresponding to a significant modification of the effective losses and energy of the molecular vibrations, respectively. These changes come together with a strong non-linear dependence of the emitted Raman signal on the intensity of the incident laser [4-6].
In this talk, a description of the molecular optomechanics approach to SERS will be given, together with an analysis of specific aspects relevant to molecular vibrations and to plasmonic modes in this context. The molecular optomechanics approach often considers a single plasmonic cavity mode, and we revise the importance of considering the full plasmonic response in the interaction [7,8]. We further consider a situation where multiple molecules are placed in the plasmonic nanocavity, giving rise to the formation of collective vibrational modes [9]. We show all these results in the context of recent experimental observations in SERS[10].
[1] Roelli, P., Galland, S. et al., 2016. Nat. Nanotech. 11, 164.[2] Schmidt, M. K., Esteban, R. et al., 2016, ACS Nano 10, 6291.[3] Esteban, R., Baumberg, J.J., Aizpurua,J., 2022. Acc. Chem. Res. 6291 [4] Schmidt, M. K. , Esteban, R. et al., 2017, Faraday Discuss. 205, 31.[5] Le Ru, E. C. and Etchegoin. 2006, P. G. Faraday Discuss. 132, 63.[6] Benz, F., et al., 2016, Science. 354, 6313.[7] Dezfouli M. K. and Hughes, S., 2017, ACS Photonics, 4, 1245.[8] Zhang, Y., Esteban. R. et al., 2021, Nanoscale 13, 1938.[9] Zhang, Y., Aizpurua. J. and Esteban, R., 2020, ACS Photonics 7, 1676.[10] Deacon, W. M., Zhang, Y. et al., submitted.
Construction and classification of symmetry protected topological phase in interacting fermion systems
Zheng-Cheng Gu [Chinese University of Hong Kong]
29 July 2022 - abstract -

Abstract:
The classification and lattice model construction of symmetry protected topological (SPT) phases in interacting fermion systems are very interesting but challenging. In this talk, I will address this problem based on the fluctuation domain wall picture. If time permits, I will also discuss classification of space group SPT phases in interacting fermion systems.

Zoom link: https://cuhk.zoom.us/j/97310017620?pwd=cDVMdndnN3N1cDVxbkVQVlk2Y20vUT09
Challenge Programs: Applied quantum computing
Phil Kaye [National Research Council of Canada]
2 June 2022
Quantum communication protocol beyond standard quantum limit
Min Namkung [Kyung Hee University]
1 June 2022 - abstract -

Abstract:
In optical communication, a sender encodes a message in an optical signal and sends it to a receiver who detects the signal to decode the message. However, the success probability or the mutual information of the conventional communication protocol cannot surpass the standard quantum limit due to the statistical and physical properties of the signal and the measurement device.

For this reason, an unconventional quantum communication protocol surpassing the standard quantum limit needs to be designed. In this talk, we provide a quantum communication protocol with an indirect measurement based on the Jaynes-Cummings model. We show that our scheme can nearly perform an optimal quantum communication enhanced by the generalization of coherent signals. Moreover, our indirect measurement can outperform the other feedback-excluded measurements in the existence of the phase-diffusion noise.

Also, enhancing the optimal success probability of N-ary unconventional quantum communication with the generalization of the coherent signal is necessary, since N-ary signal has been widely used for sending log_2N bits in one signal pulse. We show that the optimal success probability of the N-ary phase-shift-keying quantum communication can be improved by some non-sub-Poissonian, non-standard coherent state.

Reference:

[1] M. Namkung and J. S. Kim, "Enhanced Optimal Quantum Communication by Generalized Phase Shift Keying Coherent Signal", Phys. Rev. A 105, 042428 (2022).

[2] M. Namkung and J. S. Kim, "Indirect Measurement for Optimal Quantum Communication Enhanced by Binary Non-standard Coherent States", J. Opt. Soc. Am. B 39, 1247 (2022).
Locking and unlocking nonlocality without entanglement by post-measurement information
Jeong San Kim [Kyung Hee University]
31 May 2022 - abstract -

Abstract:
Nonlocality without entanglement(NLWE) is a nonlocal quantum phenomenon that arises in separable state discrimination.
In this talk, we consider the situation of discriminating quantum states from an ensemble of non-orthogonal separable states, and
show that the availability of the post-measurement information about the prepared subensemble can affect the occurrence of NLWE.
We provide a class of state ensembles consisting of four non-orthogonal separable pure states and show that the post-measurement information
about the prepared subensemble can lock(annihilate) NLWE. We also provide another class of separable state ensemble and show that the post-measurement
information can unlock(create) NLWE.

Reference

[1] Donghoon Ha and Jeong San Kim, "Annihilating and creating nonlocality without entanglement by postmeasurement information", Phys. Rev. A, 105, 022422 (2022).

[2] Donghoon Ha and Jeong San Kim, "Locking and unlocking of quantum nonlocality without entanglement in local discrimination of quantum states", Scientific Reports, 12, 3961 (2022).

2021

Semidual Kitaev lattice model and tensor network representation
Prince Osei [Quantum Leap Africa]
20 October 2021 - abstract -

Abstract:
Kitaev’s lattice models were originally proposed to exploit topological phases of matter for fault-tolerant quantum computation. They are usually defined as representations of the Drinfeld quantum double D(H), of a Hopf algebra H. In this talk, I discuss a new version based instead on M(H) a bicrossproduct quantum group, related by semidualisation to D(H). Given a finite-dimensional Hopf algebra H , we show that a quadrangulated oriented surface defines a representation of the bicrossproduct quantum group . The construction of this new model is relatively natural as it relies on the use of the covariant Hopf algebra actions. Working locally, we obtain an exactly solvable Hamiltonian for the model and provide a definition of the ground state in terms of a tensor network representation. Details may be found in https://doi.org/10.1007/JHEP09(2021)210.
Quantifying the coherence of operations and applications
Thomas Theurer [Institute for Quantum Science and Technology]
6 October 2021 - abstract -

Abstract:
Protocols and devices that exploit quantum mechanical effects can outperform their classical counterparts in certain tasks ranging from communication and computation to sensing. Intuitively speaking, the reason for this is that different physical laws allow for different technological applications. Therefore, the question where quantum mechanics differs from classical physics is not only of foundational or philosophical interest but might have technological implications too. To address it in a systematic manner, so-called quantum resource theories were developed. These are mathematical frameworks that emerge from (physically motivated) restrictions that are put on top of the laws of quantum mechanics and single out specific aspects of quantum theory as resources. In this talk, I will explain how to quantify the coherence of operations and present some recent results where this theoretical work was both applied to an actual experiment as well as interferometry.
Mechanically isolated quantum emitter in hexagonal Boron Nitride
Alexander Kubanek [University Ulm]
23 June 2021 - abstract -

Abstract:
Single photon sources are among the most crucial constituents of photonic quantum technology. Solid-state based quantum emitters are of particular importance since they offer robust and scalable platform development with potential applications in quantum information and quantum sensing. All solid-state emitters have in common, that they interact strongly with the thermal bath and lattice phonons reducing the optical and spin coherence. Therefore, solid-state quantum optics experiments are restricted to operate at cryogenic temperatures in order to suppress interactions with the solid-state environment. A measure for the optical coherence is the linewidth of an optical transition. Perfect coherence is achieved when all incoherent processes arising from interactions with the environment are suppressed. Once suppressed, the spectral line of a single photon emitter matches the Fourier Transform of its excited state decay.

In this talk I will discuss our recent investigations on defect center in hexagonal Boron Nitride. We studied more than 1000 defect centers with emission frequencies across almost the complete visible spectrum. For some of these emitters, we have observed Fourier-Transform limited lines at cryogenic temperatures under resonant excitation. We interpret our findings with the absence of any dephasing mechanism on the timescale of the scan. Surprisingly, we have discovered that these narrow optical transitions persist when increasing the temperature up to ambient conditions. Such behavior could be explained by a defect center that is decoupled from in-plane phonon modes which, in turn, could be explained by an out-of-plane defect center. I will introduce the audience to our model and understanding of the underlying physics. Furthermore, I will define characteristic features on how to identify these remarkable emitters among others.
References

[1] A. Dietrich, et al., Physical Review B, vol. 98, no.081414(R) (2018)

[2] A. Dietrich, et al., Physical Review B 101, 081401(R) (2020)

[3] M. Hoese, et al., Science Advances 6, eaba6038 (2020)

[4] S. H�u�ler, et al., arXiv:2006.13048 (2020)

[5] M. Hoese, et al., arXiv:2102.09357 (2021)
Applying Quantum Information-Theoretic Techniques to Quantum Computational Complexity
Mark Wilde [Louisiana State University]
9 June 2021 - abstract -

Abstract:
The main goal of quantum computational complexity theory is to understand the fundamental limits of computation, and the main goal of quantum information theory is to understand the fundamental limits of communication. These two fields are inevitably intertwined, given that every computational device typically makes use of communication in a non-trivial way and vice versa. In this talk, I\'ll show several ways in which we can use concepts from quantum information theory to address problems of interest in quantum complexity, focusing for the main part on the quantum interactive proof model of computation. The main concrete results I\'ll discuss are the complexity of entanglement, the complexity of recoverability of tripartite quantum states, and the complexity of testing symmetry. See https://arxiv.org/abs/1211.6120, https://arxiv.org/abs/1308.5788, and https://arxiv.org/abs/1512.05324 for background reading.
What direction is my atom pointing? (COPSS SmallTALK)
Jake Davidson [Delft University of Technology (TU Delft)]
Co-sponsored by: Calgary Optics and Photonics Student Society (COPSS)
10 March 2021 - abstract -

Abstract:
The exciting applications of quantum networking, entanglement distribution, and even classical horology promise important advances in telecommunications technology in the near future. These advances will be built upon a deep understanding of the matter systems used to build devices and carry out protocols. In this talk I will describe my recent efforts to completely characterize the magnetic effects on thulium ions in a Y3Ga5O12 (Tm:YGG) lattice. Along the way to these experimental results, I will highlight a number of experiments which have led to technological breakthroughs. Among them, I will cover how to prepare and improve atomic frequency comb quantum memories, designing atomic clocks and ion traps, and ways that we can utilize materials to improve the devices we can create. Delving into the details of the experiment itself, I will discuss our methods for measuring the hyperfine tensors of the ground (3H6) and excited (3H4) states of thulium ions in this material using a combination of spectral hole burning and optically detected nuclear magnetic resonance (ODNMR). From these techniques we measure and fit the orientation dependence of the Tm3+ ion's spin-Hamiltonian by rotating a crystal sample through a series of angles with respect to an external magnetic field. Finally with the measured spin-Hamiltonian in hand, I will highlight important crystal orientations and their impact on the applications above.
Entangled subspaces and generic local state discrimination with pre-shared entanglement
Benjamin Lovitz [University of Waterloo]
17 February 2021 - abstract -

Abstract:
It is of fundamental importance to determine the most useful entangled quantum states for non-local quantum information processing tasks. While this problem is quite well-understood in the bipartite (two-party) setting, comparatively little is known in the multipartite (more-than-two-party) setting. In this talk, we endeavour to determine the most useful entangled states for the particular task of local unambiguous state discrimination. We measure "how useful" a particular entangled state |phi> is for this task by the maximum number of generic pure states that local parties can unambiguously discriminate when they can use |phi> as a resource state to implement their local measurement. We determine that this number is equal to the Krull dimension of the Zariski closure of the set of pure states obtainable from |phi> by SLOCC. This dimension is known for several resource states, for example the GHZ state. Somewhat surprisingly, *almost all* resource states |phi> maximize this dimension, and hence are maximally useful for local state discrimination. Time permitting, we will also present related results on entangled subspaces, which are linear subspaces of multipartite space for which every element is "entangled" in some way. This talk is based on joint work with Nathaniel Johnston (arXiv:2010.02876).

2020

Quantum Photonics with hBN � from fundamental studies to emerging applications
Igor Aharonovich [University of Technology Sydney]
16 September 2020 - abstract -

Abstract:
Engineering robust solid-state quantum systems is amongst the most pressing challenges to realize scalable quantum photonic circuitry. While several 3D systems (such as diamond or silicon carbide) have been thoroughly studied, solid state emitters in two dimensional (2D) materials are still in their infancy.
In this presentation I will discuss single defects in an emerging 2D material � hexagonal boron nitride (hBN) that as promising qubits for quantum photonic applications. In particular, I will focus on ways to engineer these defects deterministically using either chemical vapour deposition growth or ion implantaiton, and show results on strain tuning of these ultra bright quantum emitters.
I will then highlight promising avenues to integrate the single defects with photonic cavities, as a first step towards integrated quantum photonics with 2D materials. I will summarize by outlining challenges and promising directions in the field of quantum emitters and nanophotonics with 2D materials.
Quasinormal modes in optics and mechanics: from Fano resonances to new insights in quantum optics
Stephen Hughes [Queen's University]
5 August 2020 - abstract -

Abstract:

Quasinormal modes (QNMs) are decaying modes of open cavity systems, with complex eigenfrequencies and spatially diverging modes. Historically, QNMs have been used to describe modes in �dirty black holes� and were scarcely even mentioned in optics. In recent years, however, QNMs they have become an extremely powerful tool for describing light-matter and force-mechanical interactions in an efficient and accurate way [1-3], and offer one of the only rigorous ways of quantizing fields in open cavity systems. While the workhorse formalism for cavity physics has been to use a �normal mode� description, for cavity modes, such an approach fails to properly account for dissipation and the phase of the mode. This talk will discuss some of the recent developments of QNMs in both optics and mechanics. Various applications will be shown, including QNMs for plasmonics, hybrid dielectric-metal systems and the elastic Purcell formula. Finally, I will also present some recent results on how to fully quantize these QNMs [4], which introduces some fundamentally new concepts in quantum optics and clearly demonstrates the limits and failure of Jaynes�Cummings type models.

[1] Philip Trost Kristensen and Stephen Hughes, Modes and Mode Volumes of Leaky Optical Cavities and Plasmonic Nanoresonators, ACS Photonics 1, 2 (2014).
[2] Mohsen Kamandar Dezfouli, Reuven Gordon, and Stephen Hughes, Modal theory of modified spontaneous emission of a quantum emitter in a hybrid plasmonic photonic-crystal cavity system, Phys. Rev. A 95, 013846 (2017).
[3] Al-Waleed El-Sayed and Stephen Hughes, Quasinormal mode theory of elastic Purcell factors and Fano resonances of optomechanical beams, arXiv:2006.14809 (2020).
[4] Sebastian Franke, Stephen Hughes, et al., Quantization of quasinormal modes for open cavities and plasmonic cavity-QED, Phys. Rev. Lett. 122, 213901 (2019); Sebastian Franke, Marten Richter, Juanjuan Ren, Andreas Knorr, and Stephen Hughes, Quantized quasinormal mode description of non-linear cavity QED effects from coupled resonators with a Fano-like resonance, arXiv:2006.04506 (2020).
Germanium color center in diamond for nanophotonic and sensing applications
Alexey Akimove [Texas A&M University]
8 July 2020 - abstract -

Abstract:

Color centers in diamond attract a lot of attention due to unique properties of diamond, such its optical and chemical purity, low concertation of nuclear spins in diamond matrix and also its physical and chemical inertness. Nitrogen vacancy (NV) color centers in diamond is the most studied color center in diamond because its fluorescence rate does depend on spin state this way enabling readout of the spin state. This property opens a lot of opportunities to for it implementation in quantum information processing [1] and sensing [2] applications. Nevertheless, NV color center has number of important disadvantages, such as broad emission spectrum dominated by phonons sideband with only 5% emission in zero-phonon sideband. Another problem is its high sensitivity to surface and structural defects in diamond often introduced by surrounding nanostructures. These disadvantages stimulated search for other color centers, which would have narrow spectrum dominated by zero-phonon line and better behavior in nanostructures.

The silicon-vacancy (SiV) center was suggested as such a center. Due to high symmetry of this center, it does not have dipole moment in the ground state and therefore is not as sensitive to various surface defects and damages as NV center. Moreover, it happens to have narrow zero-phonon line dominating the spectrum. However, unfortunately, exited state decay of this center is dominated by non-radiative relaxation. The next natural candidate is germanium-vacancy (GeV) center since Ge is right under Si in the Mendeleev table. This color center is expected to have less non-radiative decay and therefore could be good replacement for SiV. The key advantage of the group IV color centers in diamond is there relatively low sensitivity to the damages, created by nanofabrication. This opens unique opportunity to use this color centers with nanostructures photonic. It been already successfully demonstrated, that SiV containing nanocavities may significant advance performance of the color centers, making many quantum information processing possible [3,4]. In or work we are trying to make the next step in the development for such a device by integrating nanodiamonds, containing GeV color center with photonics devices out of more conventional for industry materials.

Another application of GeV color center developed by my group is temperature sensing. Again, the absolute record in combination of special resolution and sensitivity in measurement of magnetic fields and temperature belong to NV color centers in diamond. But these measurements require use of microwave radiation of Watts level which somewhat limits its applications in bioscience. We found that GeV allow different, microwave-free all-optical way of temperature measurements which is already found some application in bio community.

References
[1] M. W. Doherty, N. B. Manson, P. Delaney, F. Jelezko, J. Wrachtrup, and L. C. L. Hollenberg, Phys. Rep. 528, 1 (2013).
[2] B. K. Ofori-Okai, S. Pezzagna, K. Chang, M. Loretz, R. Schirhagl, Y. Tao, B. A. Moores, K. Groot-Berning, J. Meijer, and C. L. Degen, Phys. Rev. B - Condens. Matter Mater. Phys. 86, (2012).
[3] A. Sipahigil, R. E. Evans, D. D. Sukachev, M. J. Burek, J. Borregaard, M. K. Bhaskar, C. T. Nguyen, J. L. Pacheco, H. A. Atikian, C. Meuwly, R. M. Camacho, F. Jelezko, E. Bielejec, H. Park, M. Lončar, and M. D. Lukin, Science 354, 847 (2016).
[4] D. D. Sukachev, A. Sipahigil, C. T. Nguyen, M. K. Bhaskar, R. E. Evans, F. Jelezko, and M. D. Lukin, Phys. Rev. Lett. 119, 223602 (2017).
Security for quantum networks
Salini Karuvade [Institute for Quantum Science and Technology]
Co-sponsored by: CREATE Quanta
30 June 2020 - abstract -

Abstract:
TBA
[cancelled] Implementation of a high-fidelity Walsh-Hadamard gate with superconducting qutrits
Adrian Lupascu [University of Waterloo]
24 June 2020 - abstract -

Abstract:
We have implemented a Walsh-Hadamard gate, which realizes the quantum Fourier transform, in a superconducting qutrit. The qutrit is encoded in the lowest three energy levels of a capacitively shunted flux device. The device design combines high anharmonicity and long coherence times.\r\nThe Walsh-Hadamard gate is implemented in an optimized way, combining two unitaries, generated by off-diagonal and diagonal Hamiltonians respectively. The gate implementation utilizes simultaneous driving of all three transitions between the three pairs of energy levels of the qutrit, one of which is implemented with a two-photon process. The gate has a duration of 35 ns and an average fidelity of 99.2%, characterized with quantum state tomography. Compensation of ac-Stark and Bloch-Siegert shifts is essential for reaching high gate fidelities.\r\nWe discuss future prospects for qutrits and higher dimensionality qudits implemented with superconducting devices.
Quantum computing with cats
Alexandre Blais [University of Sherbrooke]
17 June 2020 - abstract -

Abstract:
: Since the first observation 20 years ago of first coherent quantum behaviour in a superconducting qubit there have been significant developments in the field of superconducting quantum circuits. With improvements of coherence times by over 5 orders of magnitude, it is now possible to execute increasingly complex quantum algorithms with these circuits. Despite these successes, the coherence time of superconducting devices must still be increased for quantum computation to become a reality. One approach is to improve existing devices. Another approach is to design new superconducting qubits with intrinsic protection against certain types of errors. In this talk, I will discuss how quantum information can be robustly encoded in cat states of the electromagnetic field stored in superconducting quantum devices. A feature of this encoding is that it exhibits biased noise. I will present how to realize bias-preserving gates on this qubit, and how these ideas can be further improved with quantum error correction.
Cavity QED
Farid Ghobadi [University of Calgary]
Co-sponsored by: CREATE Quanta
9 June 2020
Quantum limited amplifier (Quanta Tutorial Series)
Shabir Barzanjeh [University of Calgary]
Co-sponsored by: CREATE Quanta
26 May 2020
Quantum Emitters (Quanta Tutorial Series)
Denis Sukavech [University of Calgary]
Co-sponsored by: CREATE Quanta
19 May 2020 - abstract -

Abstract:
TBA
Waveguide-cavity coupling (Quanta Tutorial Series)
Paul Barclay [University of Calgary]
Co-sponsored by: CREATE Quanta
12 May 2020 - abstract -

Abstract:
TBA

Join Zoom Meeting https://zoom.us/j/91630960307

Meeting ID: 916 3096 0307
The power of resource theories
Carlo Maria Scandolo [University of Calgary]
Co-sponsored by: Department of Mathematics and Statistics
7 May 2020 - abstract -

Abstract:
Resource theories are a powerful framework for studying several phenomena in quantum information. In this talk, I present some of my latest research results in this area, showing how resource theories can be fruitfully employed to open new research directions, both in quantum information and beyond.

Join Zoom Meeting

https://ucalgary.zoom.us/j/95881773847

Meeting ID: 958 8177 3847
Optimal estimation of the overlap between two arbitrary quantum states
Michalis Skotiniotis [Universitat Aut�noma de Barcelona]
Co-sponsored by: Department of Mathematics and Statistics
7 May 2020 - abstract -

Abstract:
Determining the overlap, , between two arbitrary quantum states, is a fundamental primitive in quantum information processing with applications ranging from quantum fingerprinting and entanglement estimation, to quantum machine learning. Hitherto, the standard protocol for determining the overlap between two quantum states is the so-called SWAP test; given a copy of and the probability of projecting the joint state on its symmetric or antisymmetric part is determined by the overlap of the states. By repeating this measurement on several pairs of copies one can obtain a good estimate of this probability, and hence the overlap. We show that a more precise estimate can be obtained by allowing for general collective measurements on all copies. We derive the statistics of the optimal measurement and compute the optimal mean square error in the asymptotic pointwise and finite Bayesian estimation settings. We also consider two strategies relying on the estimation of one or both the states, and show that, although they are suboptimal, they outperform the SWAP test. As a bonus, we show that the optimal measurement is less invasive than the SWAP test and study the robustness to depolarizing noise for qubit states. This work is in collaboration with M. Fanizza, M. Rosati, J. Calsamiglia and V. Giovannetti. c = tr(ρσ) ρ, σ ρ σ

Join Zoom Meeting https://ucalgary.zoom.us/j/97929855495

Meeting ID: 979 2985 5495
Quantum machine learning and security on the quantum internet
Nana Liu [Shanghai Jiao Tong University]
Co-sponsored by: Department of Mathematics and Statistics
6 May 2020 - abstract -

Abstract:
The success of the modern internet relies in no small part on understanding the interplay between computation and security. More recently this area has also seen contributions from machine learning, including spam filters and malware detection. With the rising prevalence of machine learning algorithms, it is also important to address whether new security issues arise. At the same time, as quantum technologies become more accessible, these same security concerns for quantum data is expected to become more important in a future quantum internet. It then becomes intriguing to study the overlap between security and machine learning when enhanced by quantum resources.

Machine learning applications often require training or test data that originate from remote data centres or sensors. This decentralised set-up, which forms one of the application of the quantum internet, opens the door to adversaries that could exploit existing vulnerabilities in those algorithms. This incites us to ask some basic questions: What is the vulnerability of quantum machine learning algorithms? How can we exploit quantum machine learning for security purposes? We take some first key steps in addressing these questions and look towards the future of this intersection between computation and security on quantum data.

Join Zoom Meeting

https://ucalgary.zoom.us/j/95197013180

Meeting ID: 951 9701 3180

2019

Quantum gravity for the loopy
Barak Shoshany [Perimeter Institute for Theoretical Physics]
6 November 2019 - abstract -

Abstract:
Quantum gravity is one of the hardest and most important unsolved problems in physics. I will first discuss the technical and conceptual problems which arise when one tries to quantize general relativity naively, and why we want to do so in the first place. Then, I will explore and compare several of the most popular approaches to solving this problem, including string theory, loop quantum gravity, and others. I will provide a semi-technical introduction to loop quantum gravity at a level suitable for advanced undergraduates, and present its advantages and disadvantages. Finally, I will discuss my own research in loop quantum gravity, where I showed that the quantum states of discrete spacetime in loop quantum gravity, called spin networks, naturally arise from discretizing general relativity at the classical level.
How to build an efficient microwave-to-optical converter
Marcelo Wu [National Institute of Standards and Technology & University of Maryland]
13 August 2019 - abstract -

Abstract:
Superconducting qubits excel at local manipulation of quantum information. On the other hand, photonic technologies that gave us high speed fiber internet are the backbone of long-distance telecommunication. The confluence of the two spurred the recent interest in microwave-to-optical frequency converters that can efficiently and quietly transduce microwave photons from a qubit to an optical photon propagating in optical fibers and vice versa. We propose a novel approach for a converter that relies on the coupling of electrical, piezoelectric, and optomechanical resonators. We analyze the converter through the language of electrical circuits that relates device-level parameters to the overall efficiency and added noise. We then demonstrate how to design and build a converter in gallium arsenide particularly while extending our analysis to other material platforms. We will show recent progress and challenges in fabricating these transducer devices on a chip.
Hexagonal boron nitride nanophotonics
Sejeong Kim [University of Technology Sydney]
9 August 2019 - abstract -

Abstract:
Hexagonal boron nitride (hBN) has emerged as a promising platform, following reports of hyperbolic phonon-polaritons and optically stable, ultra-bright quantum emitters. In this report, we fabricate hBN into high-quality photonic devices such as photonic crystals and microrings to increase light-matter interaction. This is the first direct fabrication of van der Waals crystals into photonic devices with nano-sized features. This can open up promising avenues in many applications in nanophotonics including quantum photonics and optomechanics.
Semi-device independent quantum money
Karol Horodecki [University of Gdansk]
21 June 2019 - abstract -

Abstract:
The seminal idea of quantum money not forgeable due to laws of Quantum
Mechanics proposedby Stephen Wiesner, has laid foundations for the Quantum
Information Theory in early �70s. Recently, several other schemes for
quantum currencies have been proposed, all however relying onthe
assumption that the mint does not cooperate with the counterfeiter.
Drawing inspirations fromthe semi-device independent quantum key
distribution protocol, we introduce the first scheme ofquantum money with
this assumption partially relaxed, along with the proof of its
unforgeability.Significance of this protocol is supported by an
impossibility result, which we prove, stating thatthere is no both fully
device independent and secure money scheme. Finally, we formulate a
quantum analogue of the Oresme-Copernicus-Gresham�s law of economy.
Pauli Fusion: a computational model to realise quantum transformations from ZX terms
Niel de Beaudrap [University of Oxford]
19 June 2019 - abstract -

Abstract:
The ZX calculus is an abstract mathematical tool to represent � and importantly to calculate with � tensors of a sort that are common in quantum computational theory. We present an abstract model of quantum computation, the Pauli Fusion model, whose primitive operations correspond closely to generators of the ZX calculus (and are also straightforward abstractions of basic operations in some leading proposed quantum technologies). These operations have non-deterministic heralded effects, similarly to measurement-based quantum com- putation. We describe sufficient conditions for Pauli Fusion procedures to be deterministically realisable, so that it performs a given transformation independently of its non-deterministic outcomes. This provides an operational model to realise ZX terms beyond the circuit model.
Near-unitary spin squeezing with ytterbium
Boris Braverman [University of Ottawa]
8 March 2019 - abstract -

Abstract:
State of the art atomic sensors operate near the standard quantum limit(SQL) of projection noise, where the precision scales as the square root of the particle number. Overcoming this limit by using atom-atom entanglement such as spin squeezing is a major goal in quantum metrology. Spin squeezing can be realized by coupling an atomic ensemble to a high-finesse optical resonator, where the resulting collective atom-light interaction allows for both measurement and cavity feedback squeezing. These methods for producing spin squeezing are typically non-unitary and generate more anti-squeezing than the minimum prescribed by the uncertainty principle, due to a residual entanglement between the atomic ensemble and probing photons. We find that non-unitarity
significantly lowers the potential metrological gain from squeezing in atomic clocks and other quantum sensors.

To generate near-unitary spin squeezing experimentally, we couple an ensemble of approximately 1000 Yb-171 atoms to a high-finesse asymmetric micromirror cavity. A laser pulse induces an effective one-axis twisting Hamiltonian, producing the desired squeezed spin state, while detuning the probing light from atomic and cavity resonance by several linewidths limits the undesirable entanglement between atoms and light. We characterize the produced SSSs by
state tomography, directly observing a variance reduction of 9.4(4) dB below the SQL, limited by detection noise. For this level of squeezing, we infer a state area only 30% higher than the limit set by the uncertainty principle, confirming
the production of a nearly pure spin squeezed state. This experimental platform will allow for the creation of quantum states with metrologically useful entanglement on the clock transition of Yb-171.
Sudoku on steroids - The combinatorics of causal inference
TC Fraser [Perimeter Institute for Theoretical Physics]
20 February 2019 - abstract -

Abstract:
The objective of causal inference is to determine whether or not a system of correlated variables is compatible with a provided causal hypothesis; such hypotheses are encoded in directed acyclic graphs called causal networks. Unsurprisingly, the methodology behind causal inference is utilized in a myriad of disciplines including epidemiology, machine learning, policy making, economics and biological systems. Surprisingly, for the vast majority of small causal networks, there is no difference between the sets of compatible classical and quantum correlations, and consequently no opportunity for computational or communicational advantages. It therefore becomes incumbent to find the rare causal networks which have the capacity to support a quantum/classical separation.

In this talk, I will introduce a graphical object called a possible worlds diagram, which transforms the problem of deciding classical causal compatibility into a simple, combinatorial, constraint satisfiability game resembling Sudoku. Using several examples, I will demonstrate how to prove causal incompatibility by playing this game; including an example where no other techniques have made any progress. I will prove this approach forms a complete solution to the possibilistic causal compatibility problem and moreover, if one exploits graphical symmetries and novel consistency constraints, one can implement a hierarchy of necessary compatibility tests for the probabilistic causal compatibility problem which converges to sufficiency. Importantly, these techniques reveal which causal networks have the capacity for quantum/classical separation.
Probing spin helical surface states in topological HgTe nanowires
Johannes Ziegler [Universit�t Regensburg]
30 January 2019 - abstract -

Abstract:
The Dirac-like surface states of an ideal topological insulator nanowire form a conducting cylinder around an insulating bulk. A magnetic field applied along the wire axis modifies the 1D subband structure and results in Aharonov-Bohm oscillations. The band structure exhibits a gap for zero magnetic flux phi=0 and gapless states for half a flux quantum phi_0=h/e, which constitutes a switching from topological to trivial band structure.
Magnetotransport experiments of gated nanowires fabricated from 80 nm strained HgTe along with a theoretical analysis are presented. The widths of investigated wires range from 160 to 310 nm, with lengths of 1-2 �m. We observe phi_0=h/e periodic conductance oscillations, clearly indicating that transport is quasi-ballistic. A quantitative analysis of the gate-induced oscillations, reflecting the subband spacing, demonstrates the topological nature of the surface states.

2018

Cavity spintronics
Can-ming Hu [University of Manitoba]
18 December 2018 - abstract -

Abstract:
Cavity spintronics (also known as spin cavitronics) is a newly developing, interdisciplinary field that brings together microwave and optical communities with researchers in spintronics and magnetism. The field started around 2014 when it was found that ferromagnets in cavities hybridize with both microwaves and light by light-matter interaction [1]. Since then, the emergence of cavity spintronics has attracted broad interest from groups studying quantum electrodynamics, cavity polaritons, optomechanics, superconductivity, plasmonics, and phononics. At the center stage of the topic is the physics of magnon-photon coupling: Via the quantum physics of spin-photon entanglement on the one hand and classical electrodynamic coupling on the other, magnon-photon coupling connects some of the most exciting concepts in modern physics, such as quantum information and quantum optics, with one of the oldest sciences on earth, magnetism.

This talk aims to provide an introduction to this new frontier of condensed matter physics to researhers working in magnetism, spintronics, quantum information, and microwave technologies. The talk starts with a historical review, tracing this new field back to some of the most courageous work in the history of magnetism, spintronics, cavity quantum electrodynamics, and polaritons. Recent experiments focusing on the development of new cavity-mediated techniques, such as coupling of magnetic moments, distant manipulation of spin current, qubit-magnon coupling, and conversion between optical and microwave photons, will be highlighted.

[1] Can-Ming Hu, �Dawn of cavity spintronics,� https://arxiv.org/abs/1508.01966
On superposition, interference and Feynman paths
Urbasi Sinha [Raman Research Institute]
21 November 2018 - abstract -

Abstract:
The superposition principle forms the heart of all modern applications and properties of quantum
mechanics such as quantum entanglement and quantum computing. However, its usual application
to slit based interference experiments has caveat in both optics and quantum mechanics where it is
often incorrectly assumed that the boundary condition represented by slits opened individually is same as them being opened together. In theory work carried out over the last few years, we have
quantified the correction term in terms of the Sorkin parameter [1, 2]. In this talk, we will report the first reported measurement of a deviation from the superposition principle in the microwave domain using antennas as sources and detectors of the electromagnetic waves. This deviation is quantified through the Sorkin parameter which can be as big as 6% in our experiment [3].
Measuring a non-zero Sorkin parameter not only gives experimental verification to the theoretical
predictions about the deviation from the superposition principle in interference experiments, it
also exemplifies an experimental scenario in which non zero Sorkin parameter need not necessarily
imply falsification of Born rule for probabilities in quantum mechanics which has been the basis for
several experiments in recent years [4].

[1] R.Sawant, J.Samuel, A.Sinha, S.Sinha, U.Sinha, Non classical paths in quantum interference experiments. Phys.Rev.Lett.113,
120406 (2014).
[2] A.Sinha, Aravind H.V., U.Sinha, On the Superposition principle in interference experiments. Scientic Reports 5, 10304
(2015).
[3] G. Rengaraj, Prathwiraj U, Surya Narayana Sahoo, R. Somashekhar and Urbasi Sinha, Measuring the deviation from the
superposition principle in interference experiments, New Journal of Physics 20, 2018.
[4] U.Sinha, C.Couteau, T.Jennewein, R.La
amme, G.Weihs, Ruling out multi-order interference in quantum mechanics. Science
329, 418-421 (2010).
Towards development of a quantum network
Khabat Heshami [National Research Council of Canada]
19 November 2018 - abstract -

Abstract:
Thanks to significant progress in different aspects of quantum communications, development of continental quantum network now appears to be within reach. In this talk, I will discuss two elements contributing to such a quantum network. First, I will talk about a few recent experiments in free-space high-dimensional quantum key distribution using orbital angular momentum states of photons. In the second part of my talk, I will discuss light-matter interfaces to develop components for development of quantum networks. In particular, I will share recent results on a new approach to store photons in atomic systems and describe our progress in ultrafast modulation of photonic qubits.
Quantum simulation via all-optically generated tensor network states
Ish Dhand [University of Ulm]
3 October 2018 - abstract -

Abstract:
We devise an all-optical scheme for the generation of entangled multimode photonic states encoded in temporal modes of light. The scheme employs a nonlinear down-conversion process in an optical loop to generate one- and higher-dimensional tensor network states of light. We illustrate the principle with the generation of two different classes of entangled tensor network states and report on a variational algorithm to simulate the ground-state physics of many-body systems. We demonstrate that state-of-the-art optical devices are capable of determining the ground-state properties of the spin-1/2 Heisenberg model. Finally, implementations of the scheme are demonstrated to be robust against realistic losses and mode mismatch.
Ref: arXiv:1710.06103; Phys. Rev. Lett. 120, 130501 (2018)
Investigation of topological edge states using generalized Bloch theorem
Abhijeet Alase [Dartmouth College]
4 September 2018 - abstract -

Abstract:
The non-trivial topology of the bulk of topological insulators and superconductors manifests in the form of edge/surface states protected by discrete symmetries - a principle known as the "bulk-boundary correspondence". While our understanding of such protected states has so far largely relied on the analysis of the bulk topological properties, a main drawback of this approach is that it provides little (if any) information about the wavefunctions of the protected states, as well as their response to symmetry-breaking perturbations. We present a generalization of Bloch's theorem able to accommodate the effects of terminations and interfaces modeled by effective boundary conditions, leading to an exact algebraic solution for all energy eigenstates and eigenvalues. Using our approach, we compute analytically the energy eigenvalues and eigenstates of Su-Schrieffer- Heeger model and Kitaev's Majorana chain. We show that for certain parameter values, the Majorana modes decay exponentially in space with a power-law prefactor. We also show that the penetration depth of the chiral edge states of p+ip superconductor on a lattice diverges near those points in the surface Brillouin zone where the surface bands touch the bulk bands.
Eavesdropping a noisy radio channel by manipulation of photon bunching statistics -- theory and simulated performance
Richard Lieu [University of Alabama]
3 July 2018 - abstract -

Abstract:
The use of higher moments of an intensity time series of radio observations as extra information to improve the sensitivity of receivers is proposed. It is shown that a faint source of mean flux $\ep$ embedded in the time series of background noise of mean flux $s\gg\ep$ can be detected with increasing statistical significance if more higher moments of the time series are involved in the construction of one's flux measure, in accordance with a specific hierachical formulation. However, if $n$ is the order of the highest moment being employed then, for the method to be effective the larger the $n$ the better the resolution one must employ to sample the data. In this work we present analytical predictions of the eavesdropping performance, accompanied by numerical simulation of stationary and fully incoherent light of high occupation number (the radio limit) where the principal noise component is phase (or photon bunching) noise, to show that the predictions and simulations are in good agreement. We restricted our attention currently to the $n\ep \ll s$ limit of relatively faint sources. Sources that do not satisfy these conditions, cannot easily be modeled in analytical terms, and only further simulation effort can reveal the best way of exploiting the proposed ideas to observe them. Nevertheless, it is believed the recipe presented here opens the window to a different approach to radio data processing, one that might hold the key to the discovery of many faint sources of different types, and also such detailed radiation properties of a bright source as the coherence length of quasar emission.
Generation and application of high-quality single photons
Xianxin Guo [The Hongkong University of Science and Technology]
11 April 2018 - abstract -

Abstract:
Photon-atom interaction lies at the heart of quantum optics and quantum information processing. Working with atomic ensembles and making use of the electromagnetically induced transparency (EIT) effect, the photon-atom interaction efficiency can be significantly enhanced for exploration of unconventional phenomana. In this talk, I will report generation and application of high-quality heralded single photons from EIT-assisted four-wave mixing (FWM) in cold atomic ensembles and a hot atomic vapor cell. These photon pairs are narrowband, spectrally bright and nearly Fourier-transform limited. With these narrowband photon pairs at hand, frequency-bin entanglement can be created and tested through the Bell-CHSH inequality in a time-resolved mode. Such unique entangled photon pairs may be utilized for quantum metrology and quantum information processing. On the other hand, increasing the FWM parametric gain leads to transition from the single photon quantum regime to mirrorless optical parametric oscillation (MOPO) regime, enabling different physics such as quantum squeezing to be explored on this platform.
Dissipative quasi-local stabilization of generic pure states
Salini Karuvade [Dartmouth College]
15 March 2018 - abstract -

Abstract:
Dissipative control techniques with physically realizable resource constraints are attracting increasing attention across quantum information processing. A pure quantum state is called "dissipatively quasi-locally stabilizable" (DQLS) if it can be prepared by using purely dissipative continuous-time or discrete-time dynamics with respect to a fixed locality constraint. We characterize the DQLS nature of generic quantum states in finite dimensions for some simple yet important locality constraints, and provide conditions that must be satisfied if the states are DQLS, in more general cases. Our results shed light on approximate stabilization techniques for target pure states that are otherwise non-DQLS. Further, we describe how a state being DQLS ensures that the state is uniquely determined by its corresponding reduced states, illustrating a connection between the tasks of state preparation and local tomography. In the process, we give a constructive procedure for uniquely reconstructing a generic global state from its reduced neighborhood states, leveraging its stabilizability properties.

2017

Minimalist approach to the classification of symmetry protected topological phases
Charles Zhaoxi Xiong [Harvard University]
16 November 2017 - abstract -

Abstract:
Topological insulators and superconductors epitomize a large class of phases that fall outside Landau�s symmetry-breaking paradigm. By now it is clear that more than one phases can exist in a phase diagram even without spontaneous symmetry breaking. These are gapped phases at zero temperature distinguished by their topological properties and cannot be tuned to each other without breaking the symmetry or closing the gap. The topological properties manifest themselves in such forms as gapless boundary modes or anyonic excitations, which have garnered considerable interest due to their potential application to quantum computation.

In this talk, we will consider an interacting generalization of topological insulators and superconductors called �symmetry protected topological� (SPT) phases, which have been under intense investigation in recent years. I will first review efforts in the field to classify SPT phases, and then indicate how a seemingly abstract object in mathematics can unify various existing classification proposals and shed new light on the classification problem.

References: 1701.00004 (theoretical framework), 1709.06998 (application to hourglass fermions KHgSb)
Fundamental limitations on communication over phase-insensitive Gaussian channels
Kunal Sharma [Louisiana State University]
15 November 2017 - abstract -

Abstract:
One of the main goals of quantum information theory is to find the optimal rates of communicating classical or quantum information when allowing for quantum effects. In particular, the characterization of the quantum and private capacities of a thermal channel is of principal interest, as thermal channels model free-space communication with background thermal radiation affecting the input state, in addition to transmission loss. In our work, we establish upper bounds on the energy-constrained quantum and private capacities of the thermal channel. In this seminar talk, I will discuss three different techniques to establish our upper bounds on the energy-constrained quantum capacity of a thermal channel, and additionally, I will compare these bounds for different parameter regimes of background thermal radiation and transmission loss. I will also discuss a strategy that leads to an improved lower bound on the energy-constrained private capacity of a thermal channel.
Joint work with Mark M. Wilde (LSU), Sushovit Adhikari (LSU), and Masahiro Takeoka (NICT), and available at https://arxiv.org/abs/1708.07257.
Common resource state for preparing multi-partite quantum systems via local operations and classical communication
Cheng Guo [Tsinghua University]
1 November 2017 - abstract -

Abstract:
Given a set of multipartite entangled states, can we find a common state to prepare them by local operations and classical communication (LOCC)? Such a state, if exists, will be a common resource for this set of states. We study the properties of common resource and find the solution for bipartite case. We also point out a non-trivial common resource for 3-qubit system which is GHZ3 state.
State convertibility in the commuting operator framework
Jason Crann [Carleton University]
13 October 2017 - abstract -

Abstract:
Nielsen characterized the convertibility of two finite-dimensional bipartite pure states via local operations and classical communication (LOCC) using majorization. This important result, which has seen many applications in quantum information, describes the LOCC-transfer of entanglement between bipartite pure states. In this talk, we present a version of Nielsen's theorem in the commuting operator framework using a generalized class of LOCC operations and the theory of majorization in von Neumann algebras. As a corollary, we obtain an operational interpretation of maximal entanglement relative to von Neumann factors of type II_1.
Simulating the evolution of Markovian open quantum systems on quantum computers
Chunhao Wang [University of Waterloo]
11 October 2017 - abstract -

Abstract:
PDF
Nitrogen-vacancy centres as model systems for Quantum Hamiltonian Learning
Sebastian Knauer [University of Bristol]
27 September 2017 - abstract -

Abstract:
Efficient modelling and validation of a quantum system�s Hamiltonian - like trapped ions and atoms, quantum dots, 2D-materials, or colour centres - is intractable to classical computers, in particular when these physical systems are scaled-up or reach higher complexities ^[1]. Quantum Hamiltonian learning (QHL) is efficiently able to validate predictions for quantum systems given by model Hamiltonians ^[2]. In this approach, the exponential speed-up in reproducing the dynamics of the quantum system is given by the combination of quantum simulation with machine learning that enables to estimate the best Hamiltonian parameters among those accessible by the simulator. Here, we show for the first time, how the electron spin dynamics of an NV- centre in bulk diamond can be used to experimentally demonstrate QHL on a programmable silicon-photonics quantum simulator ^[3,4]. Primarily, this talk will focus on the experimental interfacing of both systems.
References:
1. R. P. Feynman. Simulating physics with computers. International J. of theoretical physics, 21, 467-488,1982.
2. N. Wiebe et al. Hamiltonian learning and certification using quantum resources. Phys. Rev. Lett. 112, 190501, 2014.
3. J.Wang et al. Experimental quantum Hamiltonian learning. Nat. Phys. 13:6, 551-555, 2017.
4. R. Santagati et al. Quantum simulation of Hamiltonian spectra on a silicon chip. arXiv:1611.03511, 2016.
Entanglement over Einstein: experimental violations of Bell�s inequality
Evan Meyer-Scott [University of Paderborn]
14 September 2017 - abstract -

Abstract:
Bell�s inequality provides a limit to the correlations possible in classical physics. Quantum mechanics predicts stronger correlations, but only recently have these stronger correlations been observed with a reasonably minimal set of experimental assumptions. In the first part of the talk I will present the ``loophole-free�� Bell inequality violation using entangled photon pairs from the National Institute of Standards and Technology (USA). I will then discuss future extensions to these experiments, concerning long-distance transmission and multi-party correlations. In the former, I will show how it is possible to remove some of the effects of channel loss via photonic qubit precertification, allowing the violation of Bell�s inequality even over long distance. In the latter, I will show a recent experiment verifying the time-energy entanglement of photon triplets.
An instanton laboratory for condensed matter physics
Pervez Hoodbhoy [Forman Christian College, Pakistan]
5 September 2017 - abstract -

Abstract:
Landau Levels in an inhomogeneous magnetic field imposed upon a
two dimensional free electron gas can exhibit tunneling phenomena. I will
discuss an analytical way of dealing with this and show that such a system
is ideally suited for using instantons as a theoretical tool.
Why you should not use the electric field to quantize in nonlinear optics
John Sipe [University of Toronto]
23 August 2017 - abstract -

Abstract:
We show that using the electric field as a quantization variable in nonlinear optics leads to incorrect expressions for the squeezing parameters in SPDC and conversion rates in frequency conversion. This observation is related to the fact that if the electric field is written as a linear combination of boson creation and annihilation operators one cannot satisfy Maxwell�s equations in a nonlinear dielectric.
One component quantum mechanics and target state tracing
Lianao Wu [Basque Foundation for Science]
19 July 2017 - abstract -

Abstract:
We use a Feshbach P-Q partitioning technique to derive a closed one-
component integro-differential equation for all linear system. The
resultant equation properly traces the footprint of the target state.
The
physical significance of the derived dynamical equation is illustrated by
both general analysis and concrete examples. We show that tracing a
target statel can be done by fast-changing external fields, even fast
noises. We illustrate
the results by quantum memory and controlled adiabatic paths.
Theoretical and computational aspect of entanglement and separability
Shmuel Friedland [University of Illinois at Chicago]
28 June 2017 - abstract -

Abstract:
In quantum mechanics d-partite systems are presented by d-mode tensors.Unentangled states are rank one tensors. Entangled states can be characterized their rank > 1, their spectral norm < 1 or their nuclear norm > 1. In this talk I will discuss theoretical and computational aspects of these quantities and their relevance to the entanglement and separability.
Latin squares and mutually unbiased bases
Hubert de Guise [Lakehead University]
21 June 2017 - abstract -

Abstract:
Latin squares have been studied as mathematical objects since Euler introduced the 36-ocer
problem in 1782. More recently, Fisher (amongst others) described how Latin squares can be used in
the design of experiments; Latin squares have found a host of other applications.
Mutually unbiased bases (MUBs) have a much more recent history; Wootters showed they are an
optimal choice of measurements to reconstruct the density matrix of a general quantum state. An
example of MUBs are the generalized Pauli matrices } introduced by Patera and Zassenhaus (in 1987)
in their study of gradings.
In this presentation I will describe a connection between MUBs and orthogonal Latin squares. The
common bridge linking the two are curves in discrete phase space: certain types of MUBs can be
represented by a curve, and this curve can be used to generate - under the right conditions - a Latin
square. Logical operations transforming sets of MUBs amongst themselves can transform one set of
orthogonal Latin squares into another set.
Entanglement manipulation of multipartite pure states with finite rounds of classical communication
David Sauerwein [University of Innsbruck]
9 June 2017 - abstract -

Abstract:
We consider generic pure n-qubit states and a general class of pure states of arbitrary dimensions and arbitrarily many subsystems. We characterize those states which can be reached from some other state via local operations assisted by finitely many rounds of classical communication (LOCC_N). For n qubits with n>3, we show that this set of states is of measure zero. That is, almost no state can be reached if restricted to the practical scenario of LOCC_N. We also identify classes where any separable transformation can be realized by a protocol in which each step is deterministic (all-det-LOCC_N). Such transformations can be considered as natural generalizations of bipartite transformations.
We show, however, that in general there exist state transformations which require a probabilistic step within the protocol. This highlights the difference between bipartite and multipartite LOCC and shows that multipartite LOCC transformations are more complex than the transformations considered in the literature so far.
We also analyze an interesting genuinely multipartite effect that we call locking or unlocking the power of other parties. This means that one party can prevent or enable the implementation of LOCC transformations by other parties. Finally, we show how easily computable lower bounds on some entanglement measures can be obtained by restricting to LOCC_N.

This work was published in
C. Spee, J. I. de Vicente, D. Sauerwein, and B. Kraus, Phys. Rev. Lett. 118, 040503 (2017)
J. I. de Vicente, C. Spee, D. Sauerwein, and B. Kraus Phys. Rev. A 95, 012323 (2017)
Scalable quantum nanophotonic technologies based on rare-earth-doped crystals - qubits, memories and interconnects
Tian Zhong [California Institute of Technology and University of Chicago]
7 June 2017 - abstract -

Abstract:
Rare-earth-ions in solids exhibit unusual coherence properties including
A classical counterpart for entanglement combing
Borzumehr Toloui Semnani [Southern Illinois University at Carbondale]
31 May 2017 - abstract -

Abstract:
Entanglement combing is a protocol for transforming a pure multipartite entangled state into pairs of bipartite entangled states through local operations without significant loss. Even though entanglement is an inherently quantum property, in some contexts it has an analogue in classical information theory in the form of shared classical correlation between parties and secret keys. In this talk, I describe the quantum entanglement combing protocol and a classical counterpart of it, and discuss their similarities and differences.
A fluctuation theorem for entanglement inspired by quantum information thermodynamics
Jonathan Oppenheim [University College London]
19 May 2017 - abstract -

Abstract:
TBA
Simulation of Dirac physics and fermionic topology in electromagnetics
Jianhua Jiang [Soochow University]
1 May 2017 - abstract -

Abstract:
The celebrated Dirac equation is not only the
foundation of quantum field theory, but also the parent model of many later advances in physics. One of
the key notion derived from Dirac equation is the band topology for fermions in various condensed matters.
Recently this notion is extended to bosonic systems, such as in photonics. I will briefly introduce the background, fundamental challenges and recent advances in the
search of photonic topological materials.
Band degeneracy and topology enriched by space symmetry in all dielectric photonic crystals is emphasized.
Connections with quantum optics and material sciences
will also be remarked.
Sum uncertainty relations for compact classical Lie algebras
Namrata Shukla [Institute for Quantum Science and Technology]
15 February 2017 - abstract -

Abstract:
The sum uncertainty relations are useful because they provide us with a state-independent non-trivial bound. We describe the construction of sum uncertainty relations for compact classical Lie algebras of the type su(n), so(2n), so(2n+1) and sp(n). Then we present resulting uncertainty relations explicitly for the su(2), su(3) and su(4) cases. In order to verify the bounds for general irreps of su(2) and su(3) and su(4), we develop and run a computer program that checks that the relations are correct for general states. Our method uses as a starting point the quadratic Casimir operator of the algebra, which can be recognized as a sum of variances of the generators using elementary observations. We discuss what type of states saturate the su(n) bound, and compare these states with states that saturate more familiar products of uncertainties. Our method is valuable for extending sum uncertainty relations to su(n) and beyond su(n) algebras.
Ultralow-power nonlinear optics using metastable xenon in a cavity
Garrett Hickman [University of Maryland]
3 February 2017 - abstract -

Abstract:
Single-photon cross phase shifts and other single-photon nonlinearities have numerous applications in all-optical quantum information processing. Several groups have experimentally achieved single-photon phase shifts on the order of pi. However, nonlinearities weaker than this have important applications as well. We introduce the idea of using metastable xenon gas in a high-finesse cavity to produce weak single-photon nonlinearities. This relatively simple and robust system avoids problems associated with the accumulation of alkali atoms on mirror surfaces, and is capable of approaching the strong coupling regime of cavity quantum electrodynamics. We demonstrate the feasibility of our approach with two proof-of-principle demonstrations, by measuring absorption saturation and cross-phase modulation using a cavity of moderately high finesse F=3,000. We find that the nonlinear effects occur at ultralow input power levels, proving that the presence of the cavity strongly enhances the inherent optical nonlinearities of metastable xenon. We close our discussion by reviewing our recent progress in building an improved cavity system, which is expected to produce enhanced single photon cross phase shifts.
Quantum dots in III-V semiconductor nanowires for generation of non-classical light
Dan Dalacu [National Research Council of Canada]
24 January 2017 - abstract -

Abstract:
Semiconductor quantum dots possess the critical properties required of quantum light sources for optical quantum information processing: generation of single photons, indistinguishable photons, and entangled photon pairs. The nanowire approach to quantum dot growth¹ offers several unique advantages. On one hand, the dots are readily incorporated into photonic waveguide structures that can be tailored for very efficient photon extraction and used as bright sources in secure quantum communication schemes^2,3. On the other hand, the nanowire geometry lends itself to a pick and place approach for integration with planar photonic circuits for integrated linear optical quantum computing⁴. Additionally, nanowires provide an ideal geometry for growth of perfectly aligned multiple quantum dots with monolayer control of dot-dot separation⁵. Such coupled quantum dots can be used to generate higher-order entangled states, useful in quantum repeater and optical quantum computing applications. In this presentation, I will describe a route to producing bright sources of non-classical light using InAsP quantum dots in pure phase wurtzite InP photonic nanowires.

1. D. Dalacu, et al, Nanotech. 20, 395602 (2009); D. Dalacu et al, Nano Lett. 12, 5919 (2012).

2. M.E. Reimer et al, Phys. Rev. B 93, 195316 (2016).

3. M.A.M. Versteegh et al, Nature Commun. 5, 5298 (2014); T. Huber et al, Nano Lett. 14, 7107 (2014).

4. I.E. Zadeh et al, Nano Lett. 16, 2289 (2016).
5. M. Khoshnegar et al, arXiv preprint, arXiv:1510.05898 (2015).

2016

Quantum cognition
Matthew Fisher [University of California at Santa Barbara]
15 December 2016 - abstract -

Abstract:
Putative quantum processing with nuclear spins in the wet environment of the brain would seemingly require fulﬁllment of many unrealizable conditions: for example, a common biological element with a long nuclear-spin coherence time to serve as a qubit, a mechanism for transporting this qubit throughout the brain, a molecular scale quantum memory for storing the qubits, a mechanism for quantum entangling multiple qubits, a chemical reaction that induces quantum measurements on the qubits which dictates subsequent neuron ﬁring rates, among others. My strategy, guided by these requirements, is one of reverse engineering seeking to identify the bio-chemical substrate and mechanisms hosting such putative quantum processing. Remarkably, a speciﬁc neural qubit and a unique collection of ions, molecules, enzymes and neurotransmitters is identiﬁed, illuminating an apparently single path towards nuclear spin quantum processing in the brain.
Quantum spin-mechanics: A new solid-state platform for quantum computing
Hailin Wang [University of Oregon]
5 December 2016 - abstract -

Abstract:
Mechanical degrees of freedom, often ignored or overlooked by quantum physicists, play a pivotal role in trapped ions, thus far the most successful experimental platform for quantum computing. Central to the remarkable success of the trapped ion system is the control of the collective mechanical motion at the level of a single phonon. Extending the ideas and concepts underlying the trapped-ion quantum computing paradigm to a macroscopic or mesoscopic spin-mechanical system, in which an electron spin couples strongly to a nanomechanical oscillator, opens up a new frontier for exploring quantum physics in a macroscopic system and establishes a new solid-state platform for quantum computing.

In this talk, I will discuss our recent experimental advance in developing a diamond-based spin-mechanical system. We have successfully realized a solid-state analog of trapped ions by using ground electron spin states of nitrogen vacancy (NV) centers in diamond as robust spin qubits and also by taking advantage of the strong excited-state strain coupling of NV centers for spin-mechanical coupling. We exploit adiabatic evolution of the ground spin states such that the spin qubits are subject to the excited-state strain coupling through optical interactions, but are nearly immune to decoherence of the excited state.
Nanophotonic quantum networks with silicon-vacancy color centers in diamond
Alp Sipahigil [Harvard University]
14 November 2016 - abstract -

Abstract:
Efficient interfaces between photons and quantum emitters form the basis for quantum networks and enable optical nonlinearities at the single-photon level. I will discuss recent experiments[1] where silicon-vacancy (SiV) color centers are coupled to one dimensional diamond nanophotonic devices to achieve strong light-matter interactions. By placing SiV centers inside diamond photonic crystal cavities, we realize a quantum-optical switch controlled by a single color center. We control the switch using SiV metastable states and observe optical switching at the single photon level. Raman transitions are used to realize a single-photon source with a tunable frequency and bandwidth in a diamond waveguide. By measuring intensity correlations of indistinguishable Raman photons emitted into a single waveguide, we observe a quantum interference effect resulting from the superradiant emission of two entangled SiV centers.

[1] A. Sipahigil et al., Science 10.1126/science.aah6875 (2016).
Statistical learning to estimate noise in quantum systems
Yuval Sanders [Macquarie University]
27 October 2016 - abstract -

Abstract:
Quantum computers are only valuable insofar as they can be trusted to perform properly. Yet the field of research responsible for providing techniques for establishing this trust�the field of quantum characterization, verification and validation (QCVV)�remains in its infancy. In this talk, I shall describe the potential impact of statistical learning methods on noise characterization for quantum systems. I shall present the recently released QInfer codebase and how it can be applied to at least one practical problem facing quantum computing: the characterization of unwanted resonances between a qubit and its environment.
Quantum information for quantum parameter estimation
Michail Skoteiniotis [Universitat Aut�noma de Barcelona]
26 October 2016 - abstract -

Abstract:
Parameter estimation is a pivotal task both in science and engineering. It has been known for quite some time that the use of distinctively quantum features can boost the precision of estimation of parameters, such as optical phase, frequency, magnetic fields etc, beyond that achievable by classical means. In recent years techniques from quantum information theory, both theoretical as well as experimental, have allowed us to establish rigorous lower bounds on the estimation precision, as well as explicit strategies on how to achieve these bounds. In this talk I will give a detailed description of how techniques from quantum information�in particular the use of quantum error-correcting codes and quantum control�can help boost the precision with which pertinent parameters can be estimated in the presence of general noise models. In addition, I will show how the ultimate precision limits allowed in nature, even if we assume a theory more powerful than quantum mechanics, can be determined by a single physical principle; that of no superluminal signalling.
Towards high precision frequency comb spectroscopy in the extreme ultraviolet
Gil Porat [University of Colorado]
31 August 2016 - abstract -

Abstract:
High precision spectroscopy of few-electron atoms and ions is strongly motivated by the need to test fundamental theory (e.g. quantum electrodynamics) in simple systems, amenable to precise calculation for comparison with experimental measurement. Additionally, transitions from the ground state are most susceptible to nuclear structure effects (e.g. charge radius), making them appealing as tools for testing nuclear structure theory. The frequencies of transitions from the ground state in many such systems reside in the extreme ultraviolet range of the electromagnetic spectrum (XUV, wavelengths of 10~120 nm). However, spectroscopic resolution in the XUV is severely limited by the availability of appropriate sources of XUV radiation, e.g. lasers. In this talk I will explain how precision XUV spectroscopy of helium could be used to address the open problems of the proton radius puzzle and the helium isotope charge radius difference discrepancy. Furthermore, I will discuss our experimental method of generating an XUV frequency comb laser, and our progress in scaling up the power of this laser in order to enable the highest spectroscopic precision in the XUV to date.
Classically and quantum stable emergent universe from conservation laws
Eduardo Guendelman [Ben Gurion University of the Negev]
22 August 2016 - abstract -

Abstract:
It has been recently pointed out by Mithani-Vilenkin that certain non singular models of the early universe belonging to the "emergent universe scenarios" which can be classically stable, are nevertheless unstable semiclassically to collapse. Here, we show that there is a class of emergent universes derived from scale invariant two measures theories with spontaneous symmetry breaking (s.s.b) of the scale invariance, which can have both classical stability and do not suffer the instability pointed out by Mithani-Vilenkin towards collapse. We find that this stability is due to the presence of a symmetry in the "emergent phase", which together with the non linearities of the theory, does not allow that the FLRW scale factor to be smaller that a certain minimum value in a certain protected region.
Linear-optic two-photon interference with coherent states
Gustavo Amaral [Pontifical Catholic University of Rio de Janeiro]
22 August 2016 - abstract -

Abstract:
Photon bunching is one of the most celebrated effects of two-photon interference, related to the tendency of indistinguishable photons to take the same path when there is a wave-packet overlapping in a symmetric beam splitter. We explore the two-photon interference phenomena and show that: the spectral characteristics of a light source can be determined with a high resolution Few-Photon Fourier Transform Spectroscopy which proves to be a useful asset for spectral characterization of faint optical sources below the range covered by classical heterodyne beating techniques; a sub-Poisson photon source can be constructed based on weak coherent states by time-tuning a Hong-Ou-Mandel interferometer.
What if the human brain IS a supercomputer?
Jack Tuszynski [University of Alberta]
9 August 2016 - abstract -

Abstract:
In this talk I will address the issue of the human brain's performance using physical concepts. I will discuss the power consumption and several typical clocking mechanisms for biological processes at various scales of organization. This will be assessed in view of the energy cost of information erasure. I will specifically describe subneuronal architecture of the microtubule cytoskeleton and its possible involvement in memory storage and various signaling mechanisms. Finally, I will present our recent research on the binding of anesthetics to tubulin and how this may bring in quantum physics into these considerations.
Topological quantum computation
John Bryden [Prince Mohammed University, Saudi Arabia]
5 July 2016 - abstract -

Abstract:
Michael Freedman proved that SU(2) topological quantum field theory
(TQFT) is
essentially equivalent to quantum computation. That is, quantum
computation takes
place inside a TQFT. This is demonstrated by showing that the Yang-Baxter
equation
of the system has a non-trivial braiding. It follows from this that the
unitary
transition matrices for quantum computations arise from braid group
representations.

The Artin braid groups are important objects of study in mathematics,
understanding
the representation theory of the braid groups
would solve many important problems in mathematics. In particular
understanding the
entire representation theory of the braid groups
would produce a host of new quantum invariants in dimension 3. One problem
that
plagues quantum computation is this lack of understanding about the unitary
representation ring of the braid groups. Part of my research is devoted to
understanding the representation theory of the braid groups through the
application
of stable homotopy theory in topology.

This talk will outline Freedman's idea for constructing unitary matrices
necessary for quantum computation using 0+1 dimensional topological
quantum field
theory.
Sol gel Photonics: from fabrication to application
Andrea Chiappini (CANCELLED) [Istituto di Fotonica e Nanotecnologie - CNR]
27 June 2016 - abstract -

Abstract:
The sol-gel processing is a rapidly growing area in the field of materials science owing to the potential to reduce production costs of high-quality thin films and bulk materials obtained at relatively low temperatures.The preparation of high purity stable solutions via wet chemistry allows realizing low loss glass-based planar waveguides activated with rare earth ions and fabricating 3D colloidal crystals with the aim to obtain sensitive and low cost responsive materials.In this lecture we give an overview of different confined structures such as (i) glass-ceramics planar waveguides activated with Er3+ or Tb3+ and Yb3+, (ii) responsive chromatic colloidal crystals and (iii) metallo-dielectric structures, focusing the attention on their fabrication and optical and spectroscopic features and on their possible applications.
Uncertainty relations beyond Heisenberg's
Arun Kumar Pati [Harish Chandra Research Institute, Allahabad]
16 June 2016 - abstract -

Abstract:
Heisenberg-Robertson's uncertainty relation expresses a
limitation in the possible preparations of the quantum system by giving a
lower bound to the product of the variances of two observables in terms of
their commutator. However, it does not capture the concept of incompatible
observables because it can be trivial, i.e., the lower bound can be null
even for two non-compatible observables. We prove two stronger uncertainty
relations, relating to the sum of variances, whose lower bound is
guaranteed to be nontrivial whenever the two observables are incompatible
on the state of the system. The new uncertainty relations suggest that
quantum world is more uncertain than what Heisenberg's relation entails.
Symmetry, irreversibility and information flow
David Jennings [Imperial College of London]
15 June 2016 - abstract -

Abstract:
What kinds of irreversibly can arise within a system displaying symmetry-constrained dynamics?
In this talk I shall describe research that combines symmetry principles with quantum information-theoretic notions of irreversibility. In particular, I will discuss a method of decomposing general causal processes with respect to a particular symmetry group that highlights a novel form of quantum incompatibility. This type of incompatibility relates to the consumption of abstract quantum resources and is distinct from more traditional notions such as measurement-disturbance, no-cloning and complementarity. Central to the work is an information-theoretic framework that quantifies 'asymmetry'. Such a framework has a surprisingly complex structure and provides a powerful new tool-set for a range of topics such as quantum metrology and recent approaches in quantum thermodynamics.
Quantum states with special symmetries and their connections to various branches in mathematics
Hoan Bui Dang [Institute for Quantum Science and Technology]
20 April 2016 - abstract -

Abstract:
In this talk we focus on two types of symmetric structures in Hilbert
space, namely symmetric informationally-complete POVMs (also known as
SIC states) and mutually unbiased bases (MUBs). Studies of their
symmetries have not only led to applications in quantum information, but
also revealed interesting connections to various branches in
mathematics. We will specifically describe the connections to Galois
field theory, and analytic theta functions.
Constructor Theory: Casting physics in a new form
Borzumehr Toloui Semnani []
13 April 2016 - abstract -

Abstract:
The prevailing mode of explanation in physics purports to describe everything in nature, at the most fundamental level, in terms of laws of motion and initial conditions. Constructor theory is a newly proposed alternative to this prevailing mode of explanation. The fundamental principle of constructor theory is that all laws of physics are expressible entirely in terms of what physical transformations can or cannot be caused to happen, rather than what actually will or will not happen given a particular set of initial conditions. This seemingly small change of view has dramatic consequences. For example, constructor theory treats counterfactual statements and properties and factual ones evenhandedly. This allows for information, with its counterfactual property, to have a sharp and natural expression and to be fully integrated with the rest of physics within constructor theory. Constructor theory also has a natural and efficient way to define and identify resources in terms of tasks. Yet, it has deep and important differences with conventional resource theories. While resource theories contain the same premises and ultimately the same content as their already established underlying theories in this fields, constructor theory makes independent, new and falsifiable assertions about the physical world. For example, constructor theory demands that all physical theories must have a local and deterministic structure. In this talk, I will introduce constructor theory and give a summary of its main premises and some of its early results including the newly developed constructor theory of information.
Effect of gravity on localized two-mode Gaussian quantum states
Mehdi Ahmadi [Institute for Quantum Science and Technology]
6 April 2016 - abstract -

Abstract:
We study how an arbitrary Gaussian state of two localized wave
packets, prepared in an inertial frame of reference, is described by a
pair of uniformly accelerated observers. We explicitly compute the
resulting state for arbitrarily chosen proper accelerations of the
observers and independently tuned distance between them. To do so, we
introduce a generalized Rindler frame of reference and analytically
derive the corresponding state transformation as a Gaussian channel. Our
approach provides several new insights into the phenomenon of vacuum
entanglement such as the highly nontrivial effect of spatial separation
between the observers including sudden death of entanglement. We also
calculate the fidelity of the two-mode channel for non-vacuum Gaussian
states and obtain bounds on classical and quantum capacities of a
single-mode channel. Our framework can be directly applied to any
continuous variable quantum information protocol in which the effects of
acceleration or gravity cannot be neglected.
Ideal clocks - a convenient fiction
Andrzej Dragan [University of Warsaw]
28 March 2016 - abstract -

Abstract:
We show that no device built according to the rules of quantum field theory can measure proper time along its path. Highly accelerated quantum clocks experience the Unruh effect, which inevitably influences their time rate. This contradicts the concept of an ideal clock, whose rate should only depend on the instantaneous velocity.
Relativistic quantum reference frames
Alexander Smith [University of Waterloo]
23 March 2016 - abstract -

Abstract:
Progress in physics, from Aristotelian physics, to Galilean and Newtonian physics, and then to both special and general relativity, can be viewed as a continual refinement of the notion of a reference frame. The next natural step in this progression is the idea of a quantum reference frame. In this talk, I will summarize the basic tools that have been developed to study quantum reference frames and examine how they may be applied to relativistic scenarios. In particular we will look at how two observers in different Lorentz frames that are partially correlated can communicate via the exchange of a single massive spin 1/2 particle. We will then examine an approach to quantum reference frames involving a trace over global degrees of freedom, rather than an average over all possible orientations of a system with respect to an external reference frame. This approach is anticipated to help deal with reference frames associated with non-compact groups, such as the Poincar� group.
Continuous variable surface codes: hearing a whisper in the quantum noise
Gavin Brennen [Macquarie University]
18 February 2016 - abstract -

Abstract:
Over the past decade there has been a convergence
in the fields of condensed matter and quantum information with the
discovery that many body phases of matter can used for storing and processing quantum data. The best known example of this is the qubit toric code but to date only small sized systems can be prepared in the lab. I will describe a bosonic continuous variable version of the toric code that can be prepared in large scale frequency or temporal modes of light using current technology. Such states are topologically ordered and remarkably the topological entanglement entropy can be efficiently measured in the laboratory [1]. Furthermore, these states can be used as a resource for anonymous broadcasting of classical information amoung many parties. High squeezing enables large transmission bandwidth and strong anonymity, and the topological nature of the state enables local error mitigation [2].

[1] T. Demarie, T. Linjordet, N. Menicucci, and G.K. Brennen, "Detecting Topological Entanglement Entropy in a Lattice of Quantum Harmonic Oscillators," New Journal of Physics 16, 085011 (2014).
[2] N. Menicucci, T. Demarie, and G.K. Brennen, "Anonymous broadcasting with a continuous variable topological quantum code," arXiv:1503.00717.
The quantum Blackwell theorem with some applications
Francesco Buscemi [Nagoya University]
Co-sponsored by: Pacific Instiutte for the Mathematical Sciences
17 February 2016 - abstract -

Abstract:
David Blackwell, in 1949, discovered a powerful link between game theory and statistical estimation theory by reformulating the notion of statistical sufficiency in game-theoretic terms. In this talk I will show several ways to extend Blackwell's insight to the quantum setting, describing its deep consequences in the study of quantum entanglement and nonlocality, quantum super-activation, quantum Markov chains, and, more abstractly, the role of complete positivity in quantum theory.
[CS Theory Seminar Series] Quantum correlations: Dimension bounds and conic formulations
Jamie Sikora [National University of Singapore]
22 January 2016 - abstract -

Abstract:
In this talk, I will discuss correlations that can be generated by performing local measurements on bipartite quantum systems.

I'll present an algebraic characterization of the set of quantum correlations which allows us to identify an easy-to-compute lower bound on the smallest Hilbert space dimension needed to generate a quantum correlation. I will then discuss some examples showing the tightness of our lower bound. Also, the algebraic characterization can be used to express the set of quantum correlations as the projection of an affine section of the cone of completely positive semidefinite matrices. Using this, we identify a semidefinite programming outer approximation to the set of quantum correlations which is contained in the first level of the Navascu�s, Pironio and Ac�n hierarchy, and a linear conic programming problem formulating exactly the quantum value of a nonlocal game. Time permitting, I will discuss other consequences of these conic formulations and some interesting special cases.

This talk is based on work with Antonios Varvitsiotis and Zhaohui Wei
A new paradigm for decoding quantum incompatibility
Huangjun Zhu [University of Cologne]
8 January 2016 - abstract -

Abstract:
The existence of observables that are incompatible or not
jointly measurable is a characteristic feature of quantum mechanics,
which lies at the root of a number of nonclassical phenomena, such as
uncertainty relations, wave--particle dual behavior, Bell-inequality
violation, and contextuality. However, no intuitive criterion is
available for determining the compatibility of even two (generalized)
observables, despite the overarching importance of this problem and
intensive efforts of many researchers. Here we introduce an information
theoretic paradigm together with an intuitive geometric picture for
decoding incompatible observables, starting from two simple ideas: Every
observable can only provide limited information and information is
monotonic under data processing. By virtue of quantum estimation theory,
we introduce a family of universal criteria for detecting incompatible
observables and a natural measure of incompatibility, which are
applicable to arbitrary number of arbitrary observables. Based on this
framework, we derive a family of universal measurement uncertainty
relations, provide a simple information theoretic explanation of
quantitative wave--particle duality, and offer new perspectives for
understanding Bell nonlocality, contextuality, and quantum precision limit.
Femtosecond laser nanofabrication in transparent materials
Shane Eaton [Politecnico di Milano]
7 January 2016 - abstract -

Abstract:
Focused femtosecond laser pulses drive nonlinear absorption in a wide variety of transparent materials including glasses, crystals and polymers. This nonlinear interaction enables a micrometer-sized modification confined to the focus, which allows one to pattern micro-photonic devices with novel three-dimensional geometries.In glasses and crystals, the ultrashort laser pulse interaction leads to a permanent alteration of the refractive index, enabling the formation of 3D photonic circuits. Among the many parameters used to tailor the modification in transparent materials, the pulse delivery rate is perhaps the most significant. At suitably high repetition rates, typically greater than 100 kHz, the time between pulses is shorter than time for heat from the absorbed laser pulses to diffuse out of the focal volume. This leads to an accumulation of heat at the focus and if the pulse energy is sufficiently high, the material at the focus is melted. As further pulses arrive, the size of the melted zone expands outwards. After the final incident pulse, the melt rapidly cools into a permanent modification with refractive index greater than the bulk. In this way, the dwell time in static exposures or scan speed in scanned exposures can be used to tailor the final waveguide size for a specific application. Here we will describe how high repetition rate fabrication can be exploited to form high performance and novel photonic devices in transparent materials for the burgeoning fields of quantum information, sensing and lab on a chip.

2015

Machine learning and quantum information processing: research directions and challenges
Peter Wittek [ICFO-The Institute of Photonic Sciences]
28 October 2015 - abstract -

Abstract:
Machine learning uses efficient algorithms to uncover patterns in large data sets and it fundamentally changes our perspective on data processing. Efficient algorithms strike a balance between different facets of complexity: sample size, model and computational complexities. Approaching from the domain of quantum information processing, if we would like to use the rich theory of computational learning, we have several directions to pursue. We can apply a classical learning algorithm to a physics problem or we can come up with algorithms that use quantum resources either to solve classical learning problems or an application to physics. This talk gives an introduction to the core concepts in learning theory, and then looks at the major challenges ahead in the intersection of machine learning and quantum information processing.
Realization of arbitrary discrete unitary transformations using spatial and internal modes of light
Ish Dhand [Institute for Quantum Science and Technology, University]
9 September 2015 - abstract -

Abstract:
Any lossless transformation on ns spatial and np internal modes of light can be described by an ns np � ns np unitary matrix, but no procedure to effect arbitrary ns np � ns np unitary matrix on the combined spatial and internal modes is known. We devise an algorithm to realize an arbitrary discrete unitary transformation on the combined spatial and internal degrees of freedom of light. Our realization uses beamsplitters and operations on internal modes to effect arbitrary linear transformations. The number of beamsplitters required to realize a unitary transformation is reduced as compared to existing realization by a factor equal to the dimension of the employed internal degree of freedom. Our algorithm thus enables the optical implementation of higher dimensional unitary transformations. (Based on arXiv:1508.06259)
Spacetime replication of continuous variable quantum Information
Grant Salton [Stanford University]
5 August 2015 - abstract -

Abstract:
Two basic tenets of physics that any physical theory seems to have are that (1) no information can travel faster than light and (2) quantum information cannot be cloned. Indeed, one consequence of unitarity is that quantum information cannot be replicated anywhere on a spacelike slice, yet it must replicated in a timelike direction. A set of necessary and sufficient conditions for quantum information to be replicated in spacetime was given by Hayden and May in 2012. In this talk, I'll first explain what is meant by "spacetime information replication", and then describe how one can replicate information in seemingly impossible scenarios using novel continuous variable quantum error correcting codes. I'll then present an explicit code using five bosonic modes to demonstrate the flow of information through four causal diamonds, and conclude with an experimentally feasible, optical experiment to realize this five mode error correcting code.
Finite dimensional quantum mechanics via finite geometry
Michael Revzen [Technion - Israel Institute of Technology]
29 July 2015 - abstract -

Abstract:
Introductory approach to finite affine plane geometry is given. The
geometry is used to
transcribe Hilbert space entities (operators and states) to c-number
functions in phase space.
Mutually unbiased bases are introduced and their relation to the
finite geometrical approach to underscored.
Illustrative examples formulated in detail are finite dimensional
Wigner function and Radon transform in phase space.
The geometrical interpretation for a maximally entangled states case
is outlined.
Quantum light-matter interfaces based on rare-earth-doped crystals and nano-photonics
Andrei Faraon [California Institute of Technology]
22 July 2015 - abstract -

Abstract:
Quantum light-matter interfaces that reversibly map the quantum state of photons onto the quantum states of atoms, are essential components in the quantum engineering toolbox with applications in quantum communication, computing, and quantum-enabled sensing. In this talk I present our progress towards developing on-chip quantum light-matter interfaces based on nanophotonic resonators fabricated in rare-earth-doped crystals known to exhibit the longest optical and spin coherence times in the solid state. We recently demonstrated coherent control of neodymium (Nd3+) ions coupled to yttrium orthosilicate Y2SiO5 (YSO) photonic crystal nano-beam resonator. The coupling of the Nd3+ 883 nm 4I9/2-4F3/2 transition to the nano-resonator results in a 40 fold enhancement of the transition rate (Purcell effect), and increased optical absorption (~80%) - adequate for realizing efficient optical quantum memories via cavity impedance matching. Optical coherence times T2 up to 100 μs with low spectral diffusion were measured for ions embedded in photonic crystals, which are comparable to those observed in unprocessed bulk samples. This indicates that the remarkable coherence properties of REIs are preserved during nanofabrication process. Multi-temporal mode photon storage using stimulated photon echo and atomic frequency comb (AFC) protocols were implemented in these nano-resonators. Our current technology can be readily transferred to Erbium (Er) doped YSO devices, therefore opening the possibility of efficient on-chip optical quantum memory at 1.5 μm telecom wavelength. Integration with superconducting qubits can lead to devices for reversible quantum conversion of optical photons to microwave photons.
Weak measurements via quantum erasure
Aharon Brodutch [Institute for Quantum Computing]
20 July 2015 - abstract -

Abstract:
Quantum mechanical systems with fixed past (pre-selected) and future (post-selected) boundary conditions can exhibit strange properties. In many cases the results of intermediate measurements can give seemingly paradoxical results. It may be argued that such results are counter-factual since the measurement process disturbs the relation between pre and post selection. Weak measurements provide a way to measure observables without disturbing the system thereby allowing us to make factual statements about the apparent paradoxes. For many interesting observables, however, there was no known weak measurement scheme so statements about the result of such measurements cannot be verified experimentally. Examples include non-local observables (such as the Bell observable) and sequential observables (such as those used in Leggett Garg inequalities). Recently we provided a a general scheme for performing weak measurements of a wide range of observables including non-local [1] and sequential [2] observables and illustrated the applicability of this scheme using new paradoxes that demonstrate the strange properties of quantum post-selected systems.

In this talk I will begin by reviewing the fundamental significance of weak and non-local measurements and then present the general scheme for performing non-local weak measurements [1]. I will also present a post-selection `paradox' that illustrates the significance of this scheme in both the weak and strong regime.

[1] A. Brodutch and E. Cohen, Non-local Weak Measurements via Quantum Erasure, arXiv:1409.1575 (2015).
[2] A. Brodutch and E. Cohen Weak and Strong Sequential Measurements, arXiv:1504.07628 (2015).
On the robustness of quantum bucket brigade RAM
Priyaa Varshinee Srinivasan [Institute for Quantum Science and Technology]
15 July 2015 - abstract -

Abstract:
Quantum RAM serves as an oracle which is a necessary component in the implementation of many quantum search algorithms such as Grover's search, element distinctness problem and collision finding algorithm. In 2008, Giovanni et.al. published bucket brigade architecture for quantum RAM and discussed its advantages over the fan-out architecture used by classical RAMs. They showed that a quantum RAM based on bucket brigade design consumes far lesser number of resources in terms of number of two qubit logical operations.

In our study, we analysed the bucket brigade design based on certain simple error models for Grover's search. In this talk, I would present our analysis and the results. A previous study shows that Grover's search algorithm with faulty oracle loses its quadratic speed up, which means that error correction is needed for any qRAM circuit. Our analysis shows that the resource advantage bucket brigade qRAm is lost on applying error correction to the circuit.

My talk is based on a recent paper uploaded to arXiv, which was also presented at TQC 2015.

Arunachalam, Srinivasan, Vlad Gheorghiu, Tomas Jochym-O�Connor, Michele Mosca, and Priyaa Varshinee Srinivasan. 2015. �On the Robustness of Bucket Brigade Quantum RAM.� arXiv:1502.03450, Feb.
Ultimate communication capacity of quantum optical channels
Raul Garcia-Patron [Universit� libre de Bruxelles]
13 July 2015 - abstract -

Abstract:
Optical channels, such as fibers or free-space links, are ubiquitous in today's telecommunication networks. A complete physical model of these channels must necessarily take quantum effects into account in order to determine their ultimate performances. Specifically, Gaussian bosonic quantum channels have been extensively studied over the past decades given their importance for practical purposes. In spite of this, a longstanding conjecture on the optimality of Gaussian encodings has yet prevented finding their communication capacity. In this talk we will present a recent result that solves this conjecture and establishes the ultimate achievable bit rate under an energy constraint.
On the power of coherently controlled quantum adiabatic evolutions
M�ria Kieferov� [Institute for Quantum Computing]
30 June 2015 - abstract -

Abstract:
We provide a new approach to adiabatic state preparation that uses coherent
control and measurement to average different adiabatic evolutions in ways that
cause their diabatic errors to cancel, allowing highly accurate state preparations
using less time than conventional approaches. We show that this new model for
adiabatic state preparation is polynomially equivalent to conventional adiabatic
quantum computation by providing upper bounds on the cost of simulating such
evolutions on a circuit-based quantum computer. Finally, we show that this
approach is robust to small errors in the quantum control register and that the
system remains protected against noise on the adiabatic register by the spectral
gap.
How a post-selected single photon can act like many photons
Matin Hallaji [University of Toronto]
15 June 2015 - abstract -

Abstract:
The weak nonlinear effect of a single photon on a probe beam is
studied using "weak-value amplification": by post-selecting
on a rare final state (the nearly-dark port of an interferometer), we
observe a phase shift per post-selected photon up to five times
greater than the phase shift written by a single (non-post-selected)
photon.
TBA
Kai-Mei Fu [University of Washington]
19 May 2015 - abstract -

Abstract:
TBA
QNIX: A linear optical architecture for quantum computing
Mercedes Gimeno-Segovia [Imperial College London]
24 March 2015 - abstract -

Abstract:
There is currently a great deal of effort to develop a large-scale quantum computer, and one of the most promising platforms to do so is integrated linear optics. In this talk, I will present a dynamical scheme for an integrated optics implementation of a one-way quantum computer. I will go beyond the purely theoretical work and address practical issues in order to create a physically realistic design. I will describe every step of the dynamical process, showing the outstanding issues left to be addressed and our contributions to the different stages of the dynamical process. From our contributions, I will present optimised interferometers for the generation of photonic GHZ states, a universal and scalable LOQC architecture which requires entangled sources of no more than 3 photons with no active feed-forward, and loss-tolerant and fault-tolerant strategies specifically tailored to our proposed architecture. Our work demonstrates that building a linear optical quantum computer need be less challenging than previously thought, and brings large-scale switch-free linear optical architectures for quantum computing much closer to experimental realisation.
Thermodynamics of low-temperature coherent processes
Varun Narasimhachar [University of Calgary]
11 March 2015 - abstract -

Abstract:
Extending the formalism of thermodynamics to apply to small quantum systems away from thermal equilibrium is a program that has received much interest recently. However, we still have a very limited understanding of how quantum coherence between different energy levels evolves under thermodynamic processes. Quantum coherence is especially important in exotic and useful low-temperature phenomena such as superconductivity and magnetic resonance. In this talk we report an elegant characterization of thermodynamic processes in the low-temperature regime. We call the resulting model "cooling processes", and present necessary and sufficient conditions for the feasibility of state transitions under cooling processes, including the transformation of coherence. We also present an explicit construction of low-temperature thermodynamic processes that preserve coherence to the maximum extent possible. While other recent works have provided important insights into the workings of quantum coherence in thermodynamics, our treatment enables us to find elegant and succinct conditions in the low-temperature regime. Combining the spirit of our approach with that of other works could pave the way towards a more complete understanding of coherent thermodynamics at general temperatures.

Based on our article http://arxiv.org/abs/1409.7740
Phase-locked time-and-frequency resolved homodyne detection & measuring the frequency response of an optical cavity
Katanya Brianne Kuntz [University of New South Wales]
4 March 2015 - abstract -

Abstract:
I will discuss the latest results from two experiments. First, I will discuss a simple, novel technique to measure the frequency response (free spectral range and linewidth) of an optical cavity up to 10 GHz from the optical carrier frequency without the need for a wide bandwidth photodetector. Our technique involves a fibre amplitude (intensity) modulator and a low-frequency power meter, both of which are readily available laboratory equipment.

Then I will discuss an experiment designed to characterise phase-coherent time-and-frequency resolved homodyne detection. This detection scheme can measure two optical frequency modes defined as the �symmetric� and �anti-symmetric� sideband modes. These modes are superposition states of upper and lower sideband frequencies, which are separated symmetrically in the frequency domain about the optical carrier frequency. The �symmetric� sideband mode is analogous to the amplitude quadrature, while the �anti-symmetric� sideband mode is analogous to the phase quadrature of light.

We apply phase-locked time-and-frequency resolved homodyne detection to a discretely phase modulated coherent state, and conduct MaxLik reconstruction of two distinct states: a coherent state in the �anti-symmetric� mode, and a vacuum state in the �symmetric� mode. The discrete nature of the modulation signal defines a temporal window, while the precise modulation frequency defines the demodulation frequency. We apply fixed-phase demodulation in post-processing of the captured homodyne data, which allows reconstruction of either sideband mode from a single data set.
Ergodic dynamics and thermalization in an isolated quantum system
Charles Neill [University of California, Santa Babara]
28 January 2015 - abstract -

Abstract:
Statistical mechanics is founded on the assumption that all accessible
states of a system are equally likely. This requires dynamics that explore
all configurations over time, known as ergodic dynamics. Here, using three
fully-coupled superconducting qubits, we demonstrate ergodic dynamics and
the resulting thermalization. We subject the qubits to a sequence of
periodic rotations and interactions and measure the density matrix as a
function of time. We find a striking resemblance between maps of the
entanglement entropy and the phase space dynamics in the classical limit;
classically chaotic regions coincide with regions of nearly maximum
entanglement entropy. We further show that in regions with high entropy
the qubits explore the entire accessible state space, demonstrating
quantum ergodic dynamics. In these regions, the time-averaged density
matrix approaches a microcanonical ensemble. Our work illustrates how
fundamental questions in non-equilibrium thermodynamics can be studied
using superconducting circuits.
Vibrationally enhanced quantum transport
Casey Myers [University of Queensland]
21 January 2015 - abstract -

Abstract:
The transport of quantum excitations along coupled quantum systems has received considerable attention in the literature recently, the motivation for which has been to explain the possible need for quantum mechanics in photosynthesis. For this reason researchers have been striving to answer the question of whether the presence of quantum coherence or quantum noise assists in the directed transfer of excitations in coupled systems. Recently it was shown that the transport of an excitation along a linear chain of coupled two level systems may be enhanced with a collective coupling to a driven vibrational mode. In this presentation, we first incorporate the results from quantum ratchet theory to extend this vibrationally assisted transport scheme, investigating the case of coupling to a collective vibrational mode without driving, a type of quantum Rube Goldberg machine. We find that directed transport only occurs at specific mechanical frequencies and determine the relationship between this frequency and the system parameters. Second, we investigate the presence of multiple collective driven vibrational modes to facilitate directed transport, showing that transport of excitations can occur over a broad range of mechanical driving strengths.

2014

Hyperbolic metamaterials
Zubin Jacob [University of Alberta]
Co-sponsored by: University of Calgary Nanotechnology Group
12 November 2014 - abstract -

Abstract:
In 1987, the search for a medium that expels vacuum fluctuations in a prescribed bandwidth and rigorously forbids spontaneous emission led to the concept of the photonic crystal. Here, we argue that the search for the opposite effect: enhancing vacuum and thermal fluctuations inside a medium within a prescribed bandwidth can be accomplished by an artificial medium known as a hyperbolic metamaterial. We will present the fluctuational electrodynamics of such media with hyperbolic dispersion and show that they exhibit broadband super-planckian thermal emission in the near-field. We will also present the quantum nanophotonics of hyperbolic media where the enhanced vacuum fluctuations within the medium leads to a broadband Purcell effect. Finally, we will present associated effects such as optical topological transitions which make it viable to experimentally detect the signatures of these predicted effects.

* Snacks and drinks are provided by University of Calgary Nanotechnology Group.
Can quantum mechanics resolve spacetime singularities and make the universe accelerate?
Saurya Das [University of Lethbridge]
15 October 2014 - abstract -

Abstract:
The singularity theorems in general relativity, via incompleteness of geodesics in all reasonable spacetimes, show that our universe must have singularities, where laws of physics break down, at its beginning, end or in between. Replacing classical geodesics with quantal (or Bohmian) trajectories, we show that the quantum potential they produce prevent such singularities from forming. Further we show that this potential for a condensate of gravitons gives rise to a cosmological constant with its correct observed value, and provides a viable explanation for dark energy and the late time accelerated expansion of the universe. In this picture, we also speculate on the evolution and ultimate fate of our universe.
Preserving locality in parallel applications
Priyaa Varshinee Srinivasan [University of Waterloo]
1 October 2014 - abstract -

Abstract:
Contemporary computer hardware contains high speed memory components such as cache memory, translation look aside buffer and other processor structures such as prefetchers, branch predictors that hide speed gap between main memory and processor. Usage of these resources occur transparent to operating system and is controlled in hardware. Current operating systems and applications ignore the problem optimal allocation of hardware-controlled memory resources. The problem of allocation of hardware controlled resources is closely tied to the problem software design. In this talk, I ll speak about program behavior model called the working set model that is one of the corner stones of computer science, evolution of computer hardware architecture, implications of hardware evolution on software design and methods of optimal usage of hardware controlled resources in current and future hardware. Computer hardware has undergone considerable changes in the past five decades and the direction of growth of hardware summons for new perspective on software design. My conclusions are supported by a microbenchmark and a real-world application study the results of which will be presented in the talk.
Directions for miniaturized rare-earth-ion quantum hardware
John Bartholomew [Australian National University]
6 August 2014 - abstract -

Abstract:
In the past decade, research into the solid-state rare-earth-ion system has compiled a growing resume of critical components for quantum technology. Achievements in this period include an efficient quantum memory for light¹, a non-classical light source², two-qubit gate demonstrations³, and hour-long quantum state storage⁴. However, for rare-earth-ion quantum technology to markedly outperform any classical equivalent, a miniaturized and integrable architecture must be achieved.
In this talk, I will present progress on two important aspects that will advance the goal of integrated rare-earth-ion quantum hardware. In doing so, I will also introduce the main research directions of Dr Matt Sellars' group at ANU.
One of the aims of our group is to integrate complex photonic circuitry with rare-earth-ion quantum devices on a single crystal'chip'⁵. Waveguide-based architectures are an appealing approach for achieving this goal. To assess the feasibility of waveguide devices for quantum applications requires a detailed knowledge of the ion's spectroscopic properties at the crystal surface and in highly strained regions near interfaces. Such regions of a Pr³⁺:Y₂SiO₅ sample were probed using micron resolution spectroscopic techniques. I will present the results of these experiments and the implications for designing and fabricating waveguides for rare-earth quantum technology.
An alternate route toward miniaturization is to realize devices at the single ion level. However, the extremely low fluorescence rates of rare-earth ions in solid-state hosts (10 � 1000 s ^-1) makes single ion optical detection a formidable challenge6. I will present techniques that should allow optical readout of the nuclear spin of a single rare-earth ion, and experimental progress towards this aim. These techniques allow the narrow homogeneous linewidths of bulk crystal ensembles to be maintained at the single ion level. This opens a new regime for quantum applications in these materials.
[1] Hedges et al., `Efficient Quantum Memory for Light', Nature 465, 2010.
[2] Ledingham et al., `Experimental Realization of Light with Time-Separated Correlations by Rephasing Amplified Spontaneous Emission', Physical Review Letters 109, 093602, 2012.
[3] Longdell et al., `Demonstration of Conditional Quantum Phase Shift Between Ions in a Solid', Physical Review Letters 93, 130503, 2004.
[4] Zhong et al., `Hyperfine decoherence study of Europium-doped Yttrium Orthosilicate in High Magnetic Fields', Presentation at DPC, 2013.
[5] Marzban et al., `Progress towards the development of rare-earth doped waveguides for quantum communications applications', Presentation at CLEO, 2014.
[6] Utikal et al., `Spectroscopic detection and state preparation of a single praseodymium ion in a crystal', Nature Communications 5, 2014.
Quantum non-Gaussian and Gaussian states at multiple side-band frequencies
Katanya Brianne Kuntz [University of New South Wales]
2 July 2014 - abstract -

Abstract:
We simultaneously generate photon-subtracted squeezed vacuum and squeezed vacuum at three frequencies from an optical parametric oscillator by utilizing its frequency non-degenerate sidebands. Quantum non-Gaussianity is demonstrated by applying a novel character witness.
TBA
Kai-Mei []
19 May 2014
Role of high performance computing in education
Thom Harold Dunning Jr. [University of Illinois at Urbana-Champaign]
Co-sponsored by: Centre for Molecular Simulation
16 April 2014 - abstract -

Abstract:
Scientific and engineering research has been revolutionized by computing�computer simulations provides insights and predictions unobtainable in the laboratory, computer analysis reveals unrecognized connections in collections of data, and computers control today�s most sophisticated experiments. Opportunities abound for revolutionizing teaching and learning with computing technologies. Today, however, computing has been used largely as a means to organize (e.g., Blackboard), prepare for (e.g. PowerPoint) and disseminate (e.g.,MOOCs) courses. The potential of using computing to teach students the fundamental principles of a subject through authentic computational simulation is largely unexplored.
For the past several years we have been using computational tools and simulations to help teach high school and college chemistry. We have found that the use of computational tools and simulations allows students to gain a deep and rich appreciation for the basic principles of chemistry. Further, we have found that the use of computational tools in the chemistry classroom:
� Is enthusiastically embraced by teachers and students
� Results in improved performance of both teachers and students on standard chemistry tests.
� Leads to increased student interest in chemistry.
It is time for the computing community to work with their colleagues in science and engineering to explore the use of authentic computational tools and simulations in the classroom and to develop the interfaces needed to make the tools accessible to students from middle school to graduate school.This presentation will cover the experiences that we have had using computational tools and simulations in the chemistry classroom in high schools in Illinois as well as in undergraduate organic chemistry courses at the University of Illinois.
Characterizing single photon devices for quantum information applications
Chris O'Brien [Texas A&M University]
5 March 2014 - abstract -

Abstract:
New advances in quantum information processing will require the successful construction
of single photon devices such as optical quantum memories and single photon frequency
converters. Having good theoretical models for the operation and noise characteristics of these devices are essential to their successful construction.

I will discuss two single photon devices. First, I will show how non-linear processes such as four-wave mixing introduce noise into optical quantum memories, in particular in electromagnetically induced transparency based quantum memories. Where we have shown [1] that noise due to non-linear mixing is the dominant term to the reduction of single photon storage fidelities. Understanding this noise, can lead to the creation of higher fidelity optical quantum memories.

Second, I will consider schemes for coupling superconducting quantum circuits, which show promise for scalable quantum computation, to telecom wavelength photons which are compatible with low loss optical fibers. Essentially converting a qubit from optical frequencies to a microwave excitation. This is accomplished by storing telecom photons as collective spin excitations in a rare-earth doped crystal, which are then coupled to the qubit by a microwave stripline resonator [2].

[1] N. Lauk, C. O'Brien, M. Fleischhauer, Phys. Rev. A 88, 013823 (2013).
[2] C. O'Brien, N. Lauk, S. Blum, G. Morigi, M. Fleischhauer, arXiv: 1402.5405 (2014).
Delegating private quantum computations (PIMS CRG MQI talk)
Anne Broadbent [University of Ottawa]
Co-sponsored by: The Institute for Security, Privacy and Information Assurance & PIMS CRG MQI
3 March 2014 - abstract -

Abstract:
Given the technological challenge in building quantum computers, it is likely that their initial availability will be in a client-server configuration. We address the question of privacy in this scenario, by showing that an almost-classical client can delegate the execution of any quantum computation, where the data uploaded to the server is encrypted via the one-time pad. In order to do this, the quantum power required of the client is limited to being able to prepare random BB84 states. We give a simulation-based security definition and a rigorous proof of security using a transformation to an entanglement-based protocol.
Investigating the relationship between protein dynamics and electron transfers (joint IQST-CMS seminar)
Aurelien de la Lande [Paris-Sud University]
Co-sponsored by: Center for Molecular Simulation
27 February 2014 - abstract -

Abstract:
Electron transfers (ET) are common events occurring in the course of many enzymatic reactions. Numerical approaches can play an important role in complement to experimental studies to uncover the subtle relationships between the thermodynamics and the kinetics aspects of ETs and the protein dynamics.
As an illustration, I will first present a computational study of the hydroxylation mechanism of PHM (Peptidylglycine α-Hydroxylating Monooxygenase)1 based on molecular dynamics (MD) simulations with hybrid Density Functional Theory-classical potentials (DFT/MM).2 Our study sheds new light on the catalytic cycle of this enzyme that has the ability to achieve dioxygen-dependent hydroxylation of aliphatic C-H bonds using two uncoupled metal sites between which a long range ET has to occur.3
In a second part I will present a computational study of the primary step of the photoreduction of flavin adenine mononucleotide (FAD) within a cryptochrome of plant.4 These proteins are involved in the regulation of the circadian cycles of plants or mammals, and putatively at the source of the migratory sense of birds.5 A combination of long classical MD simulations, Time-Dependent DFT calculations using long range corrected functionals and searches for empirical tunnelling pathways,6 enabled us to rationalize recent experiments performed by our collaborators.7

1: Osborne R.L.; Klinman, J. P. "Copper Oxygen Chemistry", pp 1-22; 2011, Ed. Karlin, K. D.; Itoh, S. Pub. J. Wiley & Sons.
2: Mel�a C.; Ferrer S.; Řez�č J.; Parisel O.; Reinaud O.; Moliner V.; de la Lande A. Chem. Eur. J. 2013, 19, 17328 � 17337.
3: de la Lande A.; Parisel O.; Moliner V. J. Am. Chem. Soc. 2007, 129,11700-11707.
4: Chaves, I. et al. Annu. Rev. Plant. Biol. 2011, 62, 335-364.
5: Ritz Th.; Adem S.; Schulten K. Biophys. J. 2000, 78, 707-7018
6: Cailliez F.; Gallois M.; Muller P.; de la Lande A. in preparation
7: Muller P.; Bouly J. -P.; Hitomi K.; Balland V.; Getzoff E. D.; Ritz Th.; Brettel K. Submitted
Quantum algorithms for quantum field theories
Keith Lee [Institute for Quantum Computing]
Co-sponsored by: PIMS CRG MQI Seminar Series
25 February 2014 - abstract -

Abstract:
Quantum field theory provides the framework for the Standard Model of
particle physics and plays a key role in many areas of physics. However,
calculations are generally computationally complex and limited to weak
interaction strengths. I'll describe a polynomial-time quantum algorithm
for computing relativistic scattering amplitudes in massive scalar quantum
field theories. The algorithm applies at both weak and strong coupling,
achieving exponential speedup over known classical methods at high
precision or strong coupling. I'll then present the extension of this
work to fermionic quantum field theories, the new features of which
require different techniques. The study of such quantum algorithms may
also help us learn more about the nature of quantum field theory itself.
The possibility of neuronal information processing via electrodynamic signaling in the dendritic cytoskeleton
Jack Tuszynski [University of Alberta]
18 February 2014 - abstract -

Abstract:
A model describing information processing pathways in dendrites is proposed based on
electrodynamic signaling mediated by the cytoskeleton. Our working hypothesis is that
the dendritic cytoskeleton, including both microtubules (MTs) and actin filaments plays an
active role in computations affecting neuronal function. These cytoskeletal elements are
affected by, and in turn regulate, a key element of neuronal information processing, namely,
dendritic ion channel activity. We present a molecular dynamics description of the C-termini
protruding from the surface of a MT that reveals the existence of several conformational
states, which lead to collective dynamical properties of the neuronal cytoskeleton. Furthermore, these collective states of the C-termini on MTs have a significant effect on ionic
condensation and ion cloud propagation with physical similarities to those recently found
in actin-filaments and microtubules. We also discuss experimental findings concerning both
intrinsic and ionic conductivities of microfilaments and microtubules which support
our hypothesis regarding internal processing capabilities in neurons. Our ultimate objective
is to provide an integrated view of these phenomena in a bottom-up scheme, demonstrating
that ionic wave interactions and propagation along cytoskeletal structures impacts channel
functions, and thus neuronal computational capabilities. The issue of quantum versus classical character of these interactions will be discussed. A molecular model of memory storage at a molecular level will be proposed and its implications on diseases such as Alzheimer's discussed.

2013

Majorization theory and thermodynamics (25' talk)
Varun Narasimhachar [Institute for Quantum Science and Technology]
4 December 2013 - abstract -

Abstract:
Majorization is a concept that emerges from the properties of stochastic matrices. The theory of majorization has been identified as an important tool in quantum information since its application to the theory of entanglement by Nielsen. Later works have identified other areas of quantum information where it plays a role, including thermodynamics. In this talk, we describe the connection between majorization theory and thermodynamics, with a summary of our recent results in this area. These include necessary and sufficient conditions for transitions between thermodynamic states of quantum systems, under various conditions (with or without catalysts, costing or yielding work, small or large systems). Notably, our results imply the insufficiency of the traditional formulation of the Second Law to decide the feasibility of state transitions.
On convex optimization problems in quantum information theory (25' talk)
Mark Girard [Institute for Quantum Science and Technology]
4 December 2013 - abstract -

Abstract:
The evaluation of many important quantities in quantum information theory involves finding the solution to a convex optimization problem, minimizing a convex function over a convex subset of hermitian matrices. For example, determination of the relative entropy of entanglement (REE) for an arbitrary quantum state \rho involves minimizing the relative entropy of \rho with respect to the convex set of separable states. While finding closed fomulae solutions to such convex optimization problems is usually impossible, solving the converse problem is often instructive and enlightening in regard to the original problem. That is, given a family of convex functions and a state \sigma on the boundary of a subset of hermitian matrices, we can find a closed formula for the minimum value of all functions whose minimum value is achieved at \sigma. In particular, this allows us to find explicit expressions for the REE and its variants, such as the Rains bound. This approach also elucidates interesting facts about these quantities, such that, among others, that the Rains bound reduces to the REE when at least one subsystem is a qubit.
Collapse models: from theoretical foundations to experimental verifications
Angelo Bassi [University of Trieste]
Co-sponsored by: PIMS CRG MQI Seminar Series
28 November 2013 - abstract -

Abstract:
The basic strategy underlying models of spontaneous wave function collapse (collapse models) is to modify the Schroedinger equation by including nonlinear stochastic terms, which tend to localize wave functions in space in a dynamical manner. These terms have negligible effects on microscopic systems - therefore their quantum behaviour is practically preserved. On the other end, since the strength of these new terms scales with the mass of the system, they become dominant at the macroscopic level, making sure that wave functions of macro-objects are always well-localizedc in space. Based on recent results, we discuss why modifications of the Schroedinger equation which include nonlinear stochastic terms have to be of the form used in collapse models. Therefore, in a precise sense, collapse models are the only consistent modifications of quantum mechanics, preserving general physical principles. By changing the dynamics of quantum systems, collapse models make predictions, which are different from standard quantum mechanical predictions. Although they are difficult to detect, we discuss the most relevant scenarios, where such deviations could possibly be observed.
Microcavity exciton-polariton condensates physics and applications
Na Young Kim [Stanford University]
9 October 2013 - abstract -

Abstract:
Microcavity exciton-polaritons are hybrid light-matter quasi-particles as an admixture of cavity photons and quantum well excitons. The inherent light-matter duality provides experimental advantages to form coherent condensates at high temperatures (e.g. 4 K in GaAs and room temperature in GaN materials), and to access the dynamics of exciton-polaritons.

I will first discuss the characteristics of exciton-polariton condensates with emphasis on their intrinsic open-dissipative nature. I will present exciton-polariton-lattice systems, where we explore the non-zero momentum condensate order. We envision that the polariton-lattice systems would serve as a solid-state platform to investigate strongly correlated materials. Finally, I will show our recent progress on electrically pumped exciton-polariton coherent matter waves towards the development of novel coherent light sources operating at low threshold powers and at high temperatures.
Revisiting additivity violation of quantum channels
Motohisa Fukuda [Technische Universit�t M�nchen]
Co-sponsored by: PIMS CRG MQI Seminar Series
1 October 2013 - abstract -

Abstract:
In this talk we revisit additivity violation of minimum output (von Neumann) entropy of quantum channels, which implies that entangled inputs improve the classical capacity of some quantum channels. After Hastings disproved the additivity several other proofs were made, but recently we found a proof via epsilon-net argument and Levy's lemma. Interestingly, this combination of techniques were already used by Hayden, Leung and Winter to show existence of highly entangled subspaces in a bipartite space of large dimension. Moreover, Hayden and Winter used this result to disprove the additivity of minimum output p-Renyi entropy for p>1, but the estimate was not sharp enough for p=1; von Neumann entropy. We compare the above two methods and discuss what are technical improvements to make such a concise proof on the additivity violation of minimum output entropy.
Quantum plasmonics and how to fix Purcell�s formula for spontaneous emission enhancement
Stephen Hughes [Queen's University]
19 September 2013 - abstract -

Abstract:
The study of quantum light-matter interactions near metal
cavities can be used to explore fundamental quantum optical regimes such
as modiﬁed spontaneous emission of a single photon emitter. Metal
resonators create localized surface plasmons which give rise to
pronounced resonances in a similar way to high-Q cavity structures, but
with incredibly small mode volumes. However, metal nanostructures are
signiﬁcantly more complicated to model because of material losses and
thus standard mode expansion techniques fail.

This talk will introduce several regimes of quantum nanoplasmonics with
a focus on light-matter interactions between a single quantum dot and a
metal resonator. We first show why Purcell�s formula is wrong for any
finite Q cavity [1], and we show how to unambiguously fix this formula
for any resonator including metallic cavities. We will also introduce
the phenomena of strong coupling [2] and resonance fluorescence (Mollow
triplet) of a driven quantum dot near a metal nanoparticle [3], and show
how these well known quantum optical effects are influenced by
bath-induced coupling from the metal resonator.

[1] P. Kristensen, C. Van Vlack, S. Hughes, Generalized mode volume for
leaky optical cavities, Optics Letters 37, 1649 (2012).

[2] C. Van Vlack, P. T. Kristensen, and S. Hughes, Spontaneous emission
spectra and quantum light-matter interactions from a strongly-coupled
quantum dot metal-nanoparticle system, Physical Review B 85, 0765303 (2012).

[3] Rong-Chun Ge, C. Van Vlack, P. Yao, Jeff. F. Young, S. Hughes,
Accessing quantum nanoplasmonics in a hybrid quantum-dot metal
nanosystem: Mollow triplet of a quantum dot near a metal nanoparticle,
Physical Review B 87, 205425 (2013).
Brownian motion on lie groups
Todd Kemp [University of California at San Deigo]
Co-sponsored by: PIMS MQI CRG seminar series
10 September 2013 - abstract -

Abstract:
Brownian motion is continuous random motion, discovered by early 19th Century botanist Robert Brown, studied by Albert Einstein in one of the three 1905 papers that led to his Nobel prize, and finally put on firm mathematical footing by Norbert Wiener in the 1920s. It is intimately tied to local and global geometry, and is an important tool in studying heat flow on more general manifolds.

In this talk, I will give an overview of some results on Brownian motion on classical Lie groups, focusing on unitary groups U(N) and general linear groups GL(N). I will discuss my recent work on the large-N limit of Brownian motions on these groups, their fluctuations, and applications to random matrix theory and operator algebras.
Quantum hacking
Vadim Makarov [Institute for Quantum Computing, University of Waterloo]
4 September 2013 - abstract -

Abstract:
Quantum cryptography and quantum communications, although
perfectly secure in theory, suffer from equipment imperfections that leave
possibilities for practical attacks on today's implementations. I will
introduce these attacks on an example of the detector controllability
loophole (for both avalanche photodiode and superconducting nanowire
single-photon detectors) and discuss approaches to countermeasures. I will
also show how laser damage to system components can enable eavesdropping.
On Mermin-type proofs of the Kochen-Specker theorem
Vijay Kumar Singh [Simon Fraser University]
Co-sponsored by: PIMS CRG MQI Seminar Series
21 August 2013 - abstract -

Abstract:
We discuss two approaches to producing Mermin-type proofs of the Kochen-Specker
theorem. In the first approach, one starts with a fixed set of
constraints and methods of
linear algebra are used to produce subsets that are Mermin-type
proofs. Coding theory
methods are used to gain further insight into the number of solutions
(the total number
and enumeration by weight). In the second approach, one starts with
the combinatorial
structure of the set of constraints and one looks for ways to suitably
populate this
structure with observables. As well, we are able to show that many combinatorial
structures can not produce Mermin-type proofs.
This is joint work with Petr Lisonek (SFU) and Robert Raussendorf (UBC)
Parametric amplifier development and single-shot readout of superconducting qubits
Josh Mutus [University of California at Santa Barbara]
15 August 2013 - abstract -

Abstract:
Designing amplifiers for use in a scalable, fault-tolerant quantum computer presents a host of challenges. Fault-tolerant schemes, such as the surface code, require fast, high-fidelity readout of multiple qubits. We have developed lumped-element parametric amplifiers for reading out superconducting qubits with this direction in mind. Built using wafer-scale, multi-layer fabrication techniques these single-ended parametric amplifiers allow for wider bandwidth and higher saturation performance. Additionally, our amplifiers allow for flexible operation using multiple pump modes; they operate at the quantum limit for gains exceeding 30 dB and a gain-bandwidth product greater than 500 MHz. These amplifiers are capable of 99% single-shot readout fidelity on our superconducting qubits.
Quantum computational algorithms for hidden symmetry subgroup problems
Jeong San Kim [University of Suwon]
19 July 2013 - abstract -

Abstract:
We first review the concept of Hidden Subgroup Problem (HSP) and
Hidden Symmetry Subgroup Problem (HSSP), which are algebraic formulations of various problems such as factoring, graph isomorphism and lattice problems. We then present a quantum computational algorithm for HSSP on the semi-direct product of cyclic groups $\Z_{N}\rtimes\Z_{p}$ for any odd prime p and some integer N.
Quantifying the quantum
Urbasi Sinha [Raman Research Institute]
17 July 2013 - abstract -

Abstract:
Quantum mechanics is a cornerstone of modern physics. Just as the 19th century was called the Machine Age and the 20th century the Information Age, the 21st century promises to go down in history as the Quantum Age. However, can we really claim to fully understand quantum mechanical principles? How much do we really believe of what we know? Answers to such questions require us to revisit the fundamental postulates of quantum mechanics and perform precision theoretical and experimental investigations to come up with the right bounds. In this talk, I will describe such attempts by me and others in the last few years [1,2,3]. I will describe in detail a recent theoretical result whereby we can propose table top experiments to detect non-classical paths in the Feynman path integral formalism using simple interference based experiments [4].

1. U.Sinha et al. Science 329 418 - 421, 2010.

2. I.Sollener et al. Found. Phys. 42 742 � 751, 2012.

3. D.K.Park et al. New J. Phys. 14 113025, 2012.

4. R.Sawant et al. Submitted, 2013.
Hamiltonian simulation with complexity polylogarithmic in the error
Dominic Berry [Macquarie Univeristy]
Co-sponsored by: The 10th Annual Canadian Quantum Information Students' Conference
26 June 2013 - abstract -

Abstract:
Quantum algorithms for the simulation of quantum systems described by a Hamiltonian provide an exponential improvement in speed over classical algorithms when one considers scaling of the complexity in terms of the dimension. However, one key drawback is that the scaling in terms of the allowable error, epsilon, is relatively poor. Here we provide a new quantum algorithm whose scaling with respect to the allowable error is exponentially smaller than previous algorithms. That is, the complexity is polylogarithmic in 1/epsilon, rather than polynomial. The algorithm's scaling with respect to other parameters---such as dimension and evolution time---also compares well with previous algorithms.
Study of the Electromagnetically Induced Transparency in a cold atomic ensemble and application to quantum memories
Lambert Giner [Laboratoire Kastler Brossel]
17 June 2013 - abstract -

Abstract:
In order to implement quantum communications, such as quantum cryptography,
over distances larger than one hundred of kilometers using optical fibers,
it is required to develop new tools know as "quantum repeaters". The way
those devices work is based on the development of quantum memories which
that store the quantum state of light and to retrieve it on demand.

This talk presents the realization of a quantum memory based on a cold
atomic ensemble of cesium using a protocol based on Electromagnetically
Induced Transparency (EIT). The first part of this talk describes the
realization of a magneto - optical trap producing a cold atomic cloud of
cesium exhibiting a large optical depth. The second part explains the study
of the transparency of the media. Indeed, in a Ë energy scheme, the
application of a control field on the nearby transition of the signal field
results in opening a transparency window. Two phenomena can explain this
observation: the EIT which corresponds to destructive interferences between
various excitation paths and Autler - Townes Splitting (ATS) corresponding
to the separation of the excited state into two dressed states. A
quantitative and detailed study has been carried out. The last part shows
the demonstration of the storage of a coherent state in the single photon
regime with an efficiency of 24% and the storage of a quantum information
bit encoded into the orbital momentum of light results in the single photon
regime with a fidelity larger than 92%
Efficient simulation scheme for a class of quantum optics experiments with non-negative Wigner representation
Nathan Wiebe [Institute for Quantum Computing, University of Waterloo]
29 May 2013 - abstract -

Abstract:
We provide a scheme for efficient simulation of a broad class of quantum optics experiments. Our efficient simulation extends the continuous variable Gottesman�Knill theorem to a large class of non-Gaussian mixed states, thereby demonstrating that these non-Gaussian states are not an enabling resource for exponential quantum speed-up. Our results also provide an operationally motivated interpretation of negativity as non-classicality. We apply our scheme to the case of noisy single-photon-added-thermal-states to show that this class admits states with positive Wigner function but negative P-function that are not useful resource states for quantum computation.
Quantum memories for scalable photonics
Joshua Nunn [University of Oxford]
24 April 2013 - abstract -

Abstract:
Technologies that harness the quantum properties of light could enable secure communications, improved sensing and faster computing. But photon sources, photon-photon logic gates, and photon detectors are all probabilistic, so only small-scale experiments have so far been possible. Scaling up to larger devices requires synchronising each component, which can be done with quantum memories. I will show how even inefficient memories can dramatically increase the success rate of generating photons, and I will describe experimental progress in Oxford towards implementing a quantum memory for photons in cesium vapour.
Quantum and classical signal processing with cryogenic rare earth ion dopants
Jevon Longdell [University of Otago, New Zealand]
12 February 2013 - abstract -

Abstract:
In this talk I will discuss research we are carrying out into the
applications of cryogenic rare earth ion dopants. These include
developing quantum memories and repeaters for quantum networks, working
toward single dopant detection with whispering gallery mode resonators
and creating ultrahigh selectivity optical filters for the optical
detection of ultrasound. In particular I will discuss two recent
achievements: the demonstration of rephased amplified spontaneous
emission; and separating the carrier and ultrasonic sidebands on a
scattered field with a record 49 dB selectivity. Rare earth ion dopants
4f->4f transitions are used exensively in phosphors for lighting and in
solid state laser materials. The reasons for this the low rate of
non-radiative decay for some of the optical excited states, leading to
millisecond scale lifetimes. At cryogenic (
Quantum computing on encrypted data
Krister Shalm [NIST, Boulder]
6 February 2013 - abstract -

Abstract:
With the rise of the internet we now rely on numerous remote servers and companies to process and store our personal information. The problem is that we must implicitly trust that these remote services, like Facebook and Gmail, will not abuse the information we have shared with them. The question arises about whether it is possible for a server to carry out computations on data that is encrypted. This would allow someone to use remote servers to process their sensitive data without needing to reveal any information.

In this talk I will discuss a recent protocol and experiment that solves the quantum version of this problem. With only a few extra quantum resources it is possible for a powerful quantum server to process encrypted quantum data sent from a client with a weak quantum computer. This makes it possible to build secure distributed quantum networks while protecting privacy.

2012

Continuous variable Bell inequalities
Peter Marzlin [St Francis Xavier University]
18 December 2012 - abstract -

Abstract:
Bell inequalities are relations that are fulfilled for very general classes of classical systems but are violated in quantum mechanics. They provide an upper bound for the mean value of observables which is based on only a few basic assumptions. Most Bell inequalities have been derived for observables with dichotomic spectra. We present an approach to construct Bell inequalities for continuous variable systems which employs the Moyal-Weyl representation of quantum mechanics in phase space and quantum conditional probabilities. An example of a Bell inequality violation that utilizes the non-positivity of the Wigner function is presented.
Graph Spectra and Quantum Walks
Chris Godsil [University of Waterloo]
Co-sponsored by: PIMS CRG MQI Seminar Series
12 December 2012 - abstract -

Abstract:
If A is the adjacency matrix of a graph X, then the unitary operators
defined by
U(t) = exp(-itA)
define what physicists call a continuous quantum walk. A basic problem is to
relate the physical properties of this system to features of the underlying
graph. One important question is whether for a given graph there are distinct
vertices a and b and a time t such that |U(t)_{a,b}|=1. (If this
happens we have perfect state transfer.)

My talk will provide an introduction to perfect state transfer, with an
emphasis on a number of connections with classical (or, at least, old)
problems in graph theory.
Device-independent quantum information processing
Nicolas Brunner [University of Bristol]
Co-sponsored by: PIMS CRG MQI Seminar Series
11 December 2012 - abstract -

Abstract:
In physics, experimental observations are usually described using theoretical models which make specific assumptions on the physical system under consideration. Device-independent quantum information investigates the converse approach. What can be said about a physical system from raw experimental data, that is, without making any assumptions about the system and the measurement device. Beyond the fundamental interest, these ideas are relevant for information processing, and may lead to the ultimate form of security in quantum cryptography.
Algebraic and Combinatorial Quantum Codes
Petr Lisonek [Simon Fraser University]
Co-sponsored by: PIMS CRG MQI Seminar Series
5 December 2012 - abstract -

Abstract:
We discuss some algebraic and combinatorial constructions of quantum codes. We give a variant of Construction X (known mainly from the theory of classical linear codes) that produces many new stabilizer quantum error correcting codes of lengths between 50 and 90 that have a higher minimum distance than the currently best known codes. We study entanglement assisted quantum error correcting codes arising from linear cyclic and constacyclic codes and we give an algorithm for an efficient classification of such codes when the number of e-bits is bounded. We study LDPC entanglement assisted quantum codes constructed from incidence matrices of some classes of generalized quadrangles. We give synthetic geometric constructions of counterexamples to the LU-LC Conjecture and we discuss their possible application to synthetic constructions of non-linear quantum gates. This is joint work with Vijaykumar Singh.
Spin Qubits and more in a Triple Quantum Dot Circuit
Andrew Sachrajda [National Research Council]
15 November 2012 - abstract -

Abstract:
We have developed few electron triple quantum dot devices which are suitable for quantum information applications. In this talk I will review our recent experiments in these devices. The talk will describe (i) some novel properties that a triple quantum dot system posesses such as bipolar spin blockade where spin can be evoked to transform the device into an insulator (�spinsulator�), (2) Quantum backaction where we show that sound waves generated incidentally in the device by our measurement technique can be �heard� by our qubits by a process that involves a quantum interference phenomena and (3) coherent manipulation of our qubit states. The talk will carefully describe the measurement techniques used in such investigations developed by several groups over the last decade.
Polynomial Invariants of Three-Qubit Systems
Markus Grassl [Centre for Quantum Technologies, National University of Singapore]
Co-sponsored by: PIMS CRG MQI Seminar Series
10 October 2012 - abstract -

Abstract:
Polynomial invariants provide a tool to characterise quantum states
with respect to local unitary transformations. Unfortunately, the
situation becomes very complicated already for mixed states of three
qubits due to combinatorial explosion.

After an introduction to the mathematical background and general
tools, the talk will present preliminary results for mixed quantum
states and Hamiltonians for three-qubit systems.

The talk is based on joint work in progress with Robert Zeier.
Self correcting quantum memories with a polynomial energy barrier
Kamil Michnicki [University of Washington]
Co-sponsored by: PIMS CRG MQI
26 September 2012 - abstract -

Abstract:
The ferromagnetic hard disc drive is a paradigmatic example of a self-correcting classical memory. It uses natural thermalization to passively protect against errors by encoding information in the ground state of a hamiltonian. Local errors must pass through a large energy barrier to perform a global bit flip error. Self-correcting quantum memories have the further restriction that both bit flip and phase errors must simultaneously be protected. The previous highest energy barrier for a 3-d quantum code is O(log N) where N is the number of qubits in the lattice. Whether quantum codes with power law energy barriers exist or not has been an open problem before this result. A primitive called welding is introduced which like concatenation is a method for creating new stabilizer codes from pre-existing stabilizer codes. The procedure of welding is applied to a 3-d toric code, with rough and smooth boundaries, to produce a stabilizer code with a power law minimum energy barrier, an exponential improvement over previous results.
Coherent light-atom interaction. From semi-classical to quantum.
Arturo Lezama [Universidad de la Rep�blica (Uruguay)]
29 August 2012 - abstract -

Abstract:
Several coherence spectroscopy effects are well described by the interaction of a classical field with a quantized atomic system. I review experiments on these effects, such EIT and EIA, carried in our laboratory and applications to light storage, metrology and the study of atoms under strong confinement. Later, I address recent experiments in which coherent light atom interaction results in light squeezing, a fully quantum state of the field.
Linking Asymmetry Of Quantum States To Entanglement
Borzo Toloui [IQIS, U of C]
25 July 2012 - abstract -

Abstract:
Quantum evolutions that preserve a certain symmetry are expressed as covariant transformations. We show how covariant transformations can be simulated by local operations by embedding the system's Hilbert space in the tensor product of two Hilbert spaces. The embedding maps symmetric states to separable bipartite states in the larger Hilbert space and some asymmetric states to entangled states. We show how entanglement of the bipartite image state can be used to quantify the asymmetry of the original state. Our results make it possible for the first time to construct a wide range of asymmetry monotones for general symmetry groups associated with different superselection rules, and highlights the deep links that exist between entanglement theory and the resource theories of asymmetry.
Symmetric minimal quantum tomography by successive measurements
Amir Kalev [Centre for Quantum Technologies, National University of Singapore]
19 July 2012 - abstract -

Abstract:
In this talk we consider the implementation of a symmetric
informationally complete probability-operator measurements (SIC POM)
in the Hilbert space of a d-level system by a two-step measurement
process: a diagonal-operator measurement with high-rank outcomes,
followed by a rank-1 measurement in a basis chosen in accordance with
the result of the first measurement. We find that any Heisenberg-Weyl
group-covariant SIC POM can be realized by such a sequence where the
second measurement is simply a measurement in the Fourier basis,
independent of the result of the first measurement. Furthermore, at
least for the particular cases studied, of dimension 2, 3, 4, and 8,
this scheme reveals an unexpected operational relation between
mutually unbiased bases and SIC POMs; the former are used to construct
the latter. As a laboratory application of the two-step measurement
process, we propose feasible optical experiments that would realize
SIC POMs in various dimensions.
Quantum state tomography of photosynthetic systems (joint seminar with the Institute for Biocomplexity and Informatics)
Agata Branczyk [University of Toronto]
Co-sponsored by: IBI - Institute for Biocomplexity and Informatics
18 July 2012 - abstract -

Abstract:
Recent interest in the role of quantum mechanics in the primary events of photosynthetic energy transfer has highlighted the need for better quantum-state characterization of such systems. 2D electronic spectroscopy provides a wealth of valuable insight into the system---in particular its dynamics---however, it does not yield enough information to completely characterize the state. We present a proposal for quantum state tomography of photosynthetic systems using self-calibrating tomography, which allows the reconstruction of the density matrix of the state despite incomplete knowledge of the light-matter interaction---in this case, the unknown transition dipole moments of the chromophores.

In this talk, I will provide a brief review of the emerging field of quantum effects in biology; an introduction to 2D electronic spectroscopy; and a description of our proposal for performing quantum state tomography on photosynthetic systems.
Experimental Demonstration of Adaptive Tomography
Dylan Mahler [University of Toronto]
27 June 2012 - abstract -

Abstract:
In quantum state tomography, an informationally complete set of measurements is made on N identically
prepared quantum systems and from these measurements the quantum state can be determined. In the asymptotic
limit of large N, the estimation of the state converges on the true state. The rate at which this convergence occurs
depends on both the state and the measurements used to probe the state. To characterize the quality of a set of
measurements the fidelity of the estimation with the true state, averaged over a prior distribution of states, is used as
a figure of merit. It is known that for states very close to the surface of the Bloch sphere, the average infidelity (1-F)
goes down with a rate proportional to N-1/2. It has also been shown that there exists a gap between collective
measurement protocols and local measurement protocols, but that local adaptive measurement protocols can come
close to saturating the collective measurement bound of N-1. Here we present an experimental demonstration of one
qubit tomography that achieves a rate of convergence of N-1 with only a single adaptive step and local
measurements. Efforts to extend this tomography protocol to arbitrary multipartite states are currently in progress.
Thresholds and overheads for the toric code in the presence of bit (or phase) flip errors
Fern Watson [Imperial College, London, UK]
26 June 2012 - abstract -

Abstract:
Quantum information is delicate, and as such must be protected from decoherence. Topological quantum error correcting codes are particularly robust to thermal noise, but still require active error correction. In this talk we will review one proposal for topological quantum error correction: Kitaev�s 2 dimensional toric code.

The toric code distance scales with lattice size, making a physically larger code more robust. However, in some ways a smaller code is desirable, because the experimental challenges in creating and manipulating such a state also scale with the number of qubits in the code. The overhead is a balance between these two requirements; in other words the minimum code size that will protect the state with a given accuracy, for a known error rate. We numerically investigate the overhead for the toric code and find it is logarithmic in both error rate and desired fidelity.
Phase sensitive non-linear absorption in an N system
Andal Narayanan [IQIS & Raman Research Institute]
22 June 2012 - abstract -

Abstract:
Coherent control of absorption and dispersion of electromagnetic fields by
atomic systems, is made possible using the effect of Coherent Population
Trapping (CPT). It was shown recently [1] that, the
effects of CPT in three level atomic systems connected by three
electromagnetic fields, enables the control of coherence effects induced
by any two appropriately chosen fields, through the intensity and relative
phase of the third field. In general, for a closed system made of atomic
levels and EM fields, the populations and coherences become sensitive to
the relative phase between the applied fields.

In this talk, the results of an experimental investigation of phase
dependent control, seen in such
closed three level systems, extended to an N system, will be presented [2].
It is shown that the reactive Kerr non-linearity seen traditionally in N
systems becomes phase dependent [2]. In view of this, we argue that, for
properly chosen N systems, this gives rise to the possibility of
developing an optical switch, controlled by the phase of a microwave
field.

[1] Electromagnetically induced transparency controlled by a microwave field
Hebin Li at. al, Phys. Rev. A Vol. 80, 023820 (2009)
[2] Phase sensitive microwave optical double resonance in an N system,
T.M. Preethi et. al, Euro Physics Letters, Vol. 95, 34005 (2011)
SU(3) Squeezing: quantum and semiclassical perspectives
Hubert de Guise [Lakehead University]
23 May 2012 - abstract -

Abstract:
Squeezing is well understood for harmonic oscillator and spin systems as resulting from ``non-classical�� correlations between basis states in the Hilbert space. In this talk I will introduce a definition of squeezing for SU(3) systems, illustrate how it can be understood geometrically as a generalization of the known definition, and contrast some properties of squeezing obtained from a suitable initial coherent state using the fully quantum and a semiclassical evolution generated by a Hamiltonian non-linear in the generators of the su(3) algebra.

This is collaborative work with H. Tavakoli Dinani and A. Klimov.
Hanbury Brown and Twiss and other Quantum Correlations: from Photons to Atoms
Alain Aspect [Institut d'Optique, Palaiseau, France]
27 April 2012 - abstract -

Abstract:
Fifty years ago, two astronomers, R. Hanbury Brown and R. Q. Twiss, invented a new method to measure the angular diameter of stars, below the limit set by the atmospheric fluctuations. Their proposal prompted a hot debate among physicists, and it was only after the development of R Glauber's quantum analysis that the effect was fully understood as a two particle quantum interference effect. From a modern perspective, it can be viewed as an early example of the amazing properties of pairs of quantum correlated particles.

The effect has now been observed with boson and fermion atoms, stressing its fully quantum character. After putting these experiments in a historical perspective, I will present recent results, and comment on their significance. I will also show how our individual atom detection scheme has allowed us to demonstrate the creation of atom pairs, paving the way to experiments aiming at probing entanglement in atom pairs.
Universality of the Heisenberg limit for estimates of random phase shifts
Dominic Berry [Macquarie University]
25 April 2012 - abstract -

Abstract:
The Heisenberg limit traditionally provides a lower bound on the phase uncertainty scaling as 1/N, where N is the mean number of photons in the probe. However, this limit has a number of loopholes which potentially might be exploited, to achieve measurements with even greater accuracy. We have closed these loopholes by proving a completely rigorous form of the Heisenberg limit for the average error over all phase shifts. Our result gives the first completely general, constraint-free and non-asymptotic statement of the Heisenberg limit. It holds for all phase estimation schemes, including multiple passes, nonlinear phase shifts, multimode probes, and arbitrary measurements.
Generalized Semi-Quantum Secret Sharing Schemes
Vlad Gheorghiu [IQIS and Dept. of Mathematics and Statistics, U of C]
28 March 2012 - abstract -

Abstract:
I will show that any stabilizer quantum error correcting code induces a generalized quantum secret sharing scheme with an access structure, a forbidden structure and an intermediate one. I will prove that the access structure completely determines the other two, and provide an explicit algorithm for determining the former.

I next show that the information available to the intermediate structure can be fully quantified and described by an information group, a subgroup of the Pauli group, and employ this group structure to construct a method for hiding the information from the intermediate structure via twirling of the information group and sharing of classical bits between the dealer and the players. This scheme allows the transformation of a ramp (intermediate) quantum secret sharing scheme into a semi-quantum threshold secret sharing scheme, and is optimal in the amount of classical communication required between the dealer and the players. I will illustrate the main concepts by simple examples.
New tools for exploring spins and photons in solid state nanosystems
Jesse Berezovsky [Case Western Reserve University, Cleveland]
14 March 2012 - abstract -

Abstract:
In this seminar, I will discuss novel experimental methods for optically studying spins in semiconductors. Ultrafast optical pump-probe measurement has emerged as a widespread and powerful technique for probing coherent spin phenomena in semiconductors. In recent years, however, several drawbacks to this method have become apparent. For example, short laser pulses are necessarily spectrally broad rendering high-resolution spectroscopy impossible, and the usual time-averaged detection obscures correlations between repeated measurements, which are relevant to quantum measurement questions. I will present our recent work towards overcoming these, and other problems, which have the potential to open up new materials, nanostructures, and devices to optical spin-sensitive measurement.
Gaussian Bosonic Synergy
Graeme Smith [IBM Research (NY USA)]
5 March 2012 - abstract -

Abstract:
While quantum information theory is typically studied in the
finite-dimensional regime, many real-world physical channels are best described in terms of continuous variables. The simplest such channels are gaussian bosonic channels, which result from a quadratic unitary interaction between bosonic transmission modes and an inaccessible environment in the vacuum state. This class includes good approximations of most realistic optical channels. I'll review the theory of quantum information for continuous variables, then show that the set of bosonic gaussian channels is sufficiently rich to allow superactivation: there are pairs of channels, neither of which
can transmit quantum information on its own, that can nevertheless be used together for reliable quantum communication.
Quantum measurement in living cells, and high-coherence electron bunches from cold atoms
Robert Scholten [ARC Centre of Excellence for Coherent X-ray Science, School of Physics, The University of Melbourne, Australia]
22 February 2012 - abstract -

Abstract:
�Quantum technology� normally conjures thoughts of computation and communication, but also has exciting potential applications in new ways of measuring things at the nanometre, particularly for biological systems. The nitrogen-vacancy (NV) defect centre in diamond is an especially promising single spin system for quantum measurements in biology. Our first experiments have demonstrated optically detected magnetic resonance (ODMR) of individual fluorescent nanodiamond nitrogen-vacancy centres inside living human HeLa cells, and measured their spin levels and spin coherence times while tracking their location and orientation with nanoscale precision. We have measured quantum coherence through Rabi and spin-echo sequences, and orientation with 1� angular precision, over long (>10 h) periods. Variations in the decoherence rates are linked to changes in the local environment inside the cells, representing a new non-destructive imaging modality for intracellular biology.

While quantum-based imaging is an exciting prospect, even classical imaging is a vexing problem at the atomic scale, where there is enormous potential for example to determine the structure of bio-molecules. We have recently demonstrated a new source of high-coherence electron bunches based on photoionisation of laser-cooled atoms. With laser control of the cold atom cloud, we can shape the electron bunches, and because the electrons are so cold, they retain their shape during propagation. We have created �the world�s most expensive TV�, with a new bunch shape every frame � allowing the control needed to generate ultra-high-brightness bunches for coherent diffractive imaging at nanometer and femtosecond resolution.

LP McGuinness, Y Yan, A Stacey, DA Simpson, LT Hall, D Maclaurin, S. Prawer, P Mulvaney, J Wrachtrup, F Caruso, RE Scholten and LCL Hollenberg, Nature Nanotechnology 6 358 (2011)

AJ McCulloch, DV Sheludko, M Junker, SC Bell, SD Saliba, KA Nugent and Scholten, R. E. Nature Physics 7 785 (2011)
Robust cluster state generation using ancilla-based systems
Viv Kendon [University of Leeds, UK]
22 February 2012 - abstract -

Abstract:
Efficient generation of cluster states is crucial for engineering large-scale measurement-based quantum computers. Hybrid matter-optical systems offer a robust, scalable path to this goal. Such systems have an ancilla which acts as a bus connecting the qubits. We show that by generating the cluster in smaller sections of interlocking bricks, reusing one ancilla per brick, the cluster can be produced with maximal efficiency, requiring fewer than half the operations compared with no bus reuse. By reducing the time required to prepare sections of the cluster, bus reuse more than doubles the size of the computational workspace that can be used before decoherence effects dominate. A row of buses in parallel provides fully scalable cluster-state generation requiring only 20 controlled-PHASE gates per bus use. Similar efficiencies are obtained for other quantum computations, including a linear QFT, implying that qubus quantum computing is equivalent to the circuit model with unbounded fan-out.
Non-linear optics using Rydberg atoms
Charles Adams [Durham University, UK]
15 February 2012 - abstract -

Abstract:
We present recent work on cooperative non-linear optics where the non-
linearity is mediated not directly by the interaction between light
and matter, but indirectly by dipole-dipole interactions between light
induced excitations. For the giant dipoles associated with transitions
between highly excited Rydberg states, a single excitation induces a
cooperative response of up to 1000 neighboring atoms, thereby greatly
amplifying the effect of each photon. This amplifying mechanism
results in strongly enhanced optical non-linearities, see J. D.
Pritchard et al. Phys. Rev. Lett. 105, 193603 (2010), allowing the
creation and control of non-classical states of light.
Manipulating Optical Properties by Local-Field Effects and Nanostructuring
Ksenia Dolgaleva [Department of Electrical and Computer Engineering, University of Toronto]
Co-sponsored by: Electrical and Computer Engineering
8 February 2012 - abstract -

Abstract:
Local electric field, driving the atomic transition in an optical material is, in general, different from the macroscopic field in the medium. It contains the contributions from the fields of the surrounding atoms or molecules. An even more interesting situation arises in case of nanocomposite optical materials, which are nanoscale mixtures of two or more homogeneous constituents, where the morphology can significantly modify the local field. In this talk, I will discuss how local-field effects and nanostructuring can be utilized for manipulating the optical properties of nanocomposite materials. I will also talk about some opportunities that local-field effects offer in the nonlinear optical regime. Among those is, for example, the microscopic cascaded contribution of the lower-order nonlinearities to the higher-order nonlinear response. There can exists new phenomena that local-field effects are yet to offer, and research in this field can bring up many practical applications.
Robustness of adiabatic quantum computation against decoherence
Mohammad Amin [IQC, DWave Systems]
Co-sponsored by: PIMS CRG MQI Seminar Series
25 January 2012 - abstract -

Abstract:
Decoherence is widely regarded as the most significant obstacle in the development of quantum computers. Without complex and costly error correction schemes, most forms of quantum computation must be completed within a short decoherence time, significantly limiting their applicability. Adiabatic quantum computation (AQC), however, is a quantum computation scheme that is believed to be more robust against decoherence. In this talk, I will start by introducing AQC as a scheme for quantum computation, with an emphasis on its inherent tolerance towards environmental noise. I then demonstrate a hardware implementation of AQC using superconducting flux qubits, and present experimental results from the operation of a 16 qubit block of a 128-qubit superconducting quantum processor. The results show not only tolerance against environmental noise, but also significant enhancement of performance from weakly coupling to a thermal environment. All results are shown to be in close agreement with quantum mechanical predictions.
Quantum System Identification: Hamiltonian tomography and decoherence estimation from noisy time series data
Sophie Schirmer [College of Science (Physics), Swansea University]
16 January 2012 - abstract -

Abstract:
I will discuss ways to characterize the dynamics of a quantum system given a restricted set of initial states that can be prepared and a very limited set of available measurements. I will first discuss strategies for Hamiltonian identification using Bayesian parameter estimation from noisy time series data, level structure identification and finally Hamiltonian reconstruction. I will then consider how to generalize this approach to open systems in special cases, e.g., to estimate dephasing rates, and possible alternatives.

References -- recent:

http://arxiv.org/abs/1012.4593
http://arxiv.org/abs/0911.1367
http://arxiv.org/abs/0911.5429
http://arxiv.org/abs/0805.2725
http://arxiv.org/abs/quant-ph/0702123

and a link to the first one we did on this for 2-level systems:

http://www.damtp.cam.ac.uk/user/sgs29/research/papers/PRA69n050306R.pdf

2011

Density of States of Quantum Spin Systems
Ramis Movassagh [MIT]
22 December 2011 - abstract -

Abstract:
We propose a method which we call "Isotropic Entanglement" (IE), that predicts the eigenvalue distribution of quantum many body (spin) systems (QMBS) with generic interactions. We interpolate between two known approximations by matching fourth moments. Though, such problems can be QMA-complete, our examples show that IE provides an accurate picture of the spectra well beyond what one expects from the first four moments alone. We further show that the interpolation is universal, i.e., independent of the choice of local terms.
Measuring Quantum Correlations with Imperfect Photoncounters
Si-Hui Tan [Data Storage Institute - Singapore]
21 December 2011 - abstract -

Abstract:
The recent emergence of photon-number-resolving detectors (PNRDs) makes the characterization of multiphoton states via photoncounting possible. Here I will discuss several popular types of PNRDs and show how we can model realistic PNRDs using positive-operator valued measures. I apply this model to the measurement of quantum correlations and the calibration of these PNRDs.
What can we know from weak measurements?
Shengjun Wu [Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China]
7 December 2011 - abstract -

Abstract:
The idea of weak measurement was introduced by Aharonov, Albert and Vaidman in 1988. It not only provides a theoretical framework for addressing counterintuitive quantum phenomena and fundamental questions, but also gives a practical tool for amplifying very tiny signals that would not be observed in the conventional measurement schemes. In this talk, I shall review the basic idea of weak measurement, and show explicitly how it can be used for signal amplification. I shall present an extension of weak measurement to general preselection and postselection with corrections to high order terms, and give a general formalism for weak measurement of a pair of complementary observables. I shall also discuss the limitation on amplification of the signal-to-noise ratio and how this limitation can be overcome by simultaneous weak measurements of a pair of complementary observables. An experimental scheme based on parametric down conversion will be presented. This scheme could also work in other processes such as the opto-mechanical interaction in the strong coupling regime and the four-wave mixing process in cold atoms.
Triple slits, Born Rule and beyond...
Urbasi Sinha [IQC (University of Waterloo)]
29 November 2011 - abstract -

Abstract:
The first experiment describes a precision test for Born rule for probabilities in quantum
mechanics. The quadratic nature of the Born probability expression entails that interference
occurs in pairs of paths. We tested the correctness of Born rule by testing for the presence or
absence of genuine three-path interference using single photons and a triple slit aperture.
The consequences of a detection of even a small three-way interference in the quantum
mechanical null prediction are tremendous. A non-zero result would mean that quantum
mechanics is only approximate; in the same way that the double slit experiment proves that
classical physics is only an approximation to the true law of nature. This would give us an
important hint on how to generalize quantum mechanics and open a new window to the world.
In this talk, I will show results that bound the possible violation of Born�s rule and multi-path
interference in quantum mechanics and will point out ways to obtain a tighter experimental
bound.[1,2,3,4]
Next I will describe the usage of the triple slit system to demonstrate a stable Young-type
photonic qutrit. We have used our qutrit system to perform the first ever experimental
verification of the Aharon-Vaidman quantum game which exemplifies the advantage of using
simple quantum systems to outperform classical strategies. [5]
The global and local additivity problems in quantum information theory
Shmuel Friedland [University of Illinois, Chicago ]
Co-sponsored by: PIMS CRG MQI Seminar Series
9 November 2011 - abstract -

Abstract:
The capacity of the classical channel was investigated by Claude Shannon in 1948. This capacity is additive under the tensor products of two channels. The capacity of a quantum channel (QC) was introduced by Alexander Holevo in 1998. One of the fundamental problems in quantum information theory is whether the capacity of QC is additive or not under the tensor product. Equivalently, can entangled input increase the quantum capacity?
In 2009 Matthew Hastings gave a positive answer to this problem!

It was shown by Peter Shor in 2004 that the additivity of the Holevo capacity is equivalent to:
- additivity of the minimum entropy output of a quantum channel,
- additivity of the entanglement of formation,
- strong superadditivity of the entanglement of formation.

Contrary to the above result we will show that the local minimum entropy output of a quantum channel is additive. This result is a joint work with Gilad Gour.
Measuring the Hall effect for ultracold atoms in a synthetic magnetic field
Lindsay LeBlanc [Joint Quantum Institute (JQI), National Institute of Standards and Technology (NIST), and University of Maryland]
26 October 2011 - abstract -

Abstract:
As ultracold atoms experiments move towards realistic quantum
simulations of many-body physics problems, new techniques are being
developed to increase the complexity of these systems. While the
effects of real electric or magnetic fields are absent due to the
electrical neutrality of the atoms commonly used, recent experiments
have demonstrated how atom-light coupling can be used to generate
synthetic electric and magnetic fields [1]. In the scheme presented
here, the spatial dependence of a Raman coupling between levels of the
ground state manifold for our 87Rb atoms provides the necessary
relationship between internal (spin) and external (momentum) degrees
of freedom to generate a synthetic magnetic field and associated
Lorentz-like force. We measured the Hall effect in a Bose-Einstein
condensate by studying its transport in the presence of the synthetic
field. These measurements reveal internal properties of the system,
much as the Hall effect is used to study solid-state systems, and
demonstrate the utility of this technique as a probe of ultracold
ensembles.
IQIS welcome party
IQIS Faculty [IQIS]
28 September 2011 - abstract -

Abstract:
You are invited to the IQIS welcome party on Wednesday, September 28, at 3:00pm-5:00pm in SB 144. Light snack, pop, tea, and coffee will be served. �Come and celebrate our new�members, graduated and graduating members and welcome everyone back from holidays. �Three of our newer Faculty members�Paul Barclay,�Dennis Salahub and�Renate Scheidler�will each give a presentation on their work and its relation to IQIS. �This is an opportunity to learn about their work, to mingle, and to start on a new exciting year! �The schedule for the event is

3:00-3:05 Welcome
3:05-3:25 Paul Barclay presentation
"Nanoscale photonics for probing artificial atoms and other quantum systems"
A longstanding goal among quantum physicists is the development of optical circuits connecting quantum systems, allowing small numbers of photons to create entanglement between quantum "nodes." In this talk I will present my contributions to this effort, and discuss how the nanoscale photonic components that I study can also be excellent sensors and ultralow power information processing elements.
3:25-3:45 Dennis Salahub�presentation
"Wanderings and wonderings of a quantum chemist in the coherent/decoherent world of biology"
I will try to hit the highlights of a multiscale approach to electron transfer in biology. This started out about 4 or 5 years ago with discussions amongst Stu Kauffman, Barry Sanders, Nathan Babcock, Aur�lien de la Lande, Honza Řez�č and myself. Nathan, Aurelien and Honza settled on the problem of understanding the electron transfer between two proteins and they did some very nice work using Molecular Dynamics and an empirical pathway model that brought out the crucial role of water molecules in the interfacial region between the donor protein and the acceptor (published in PNAS). We are now digging deeper into the nature of the non-adiabatic terms that determine the transfer rate, within the framework of the two-state Marcus theory and decoherence theory.
3:45-4:15 Light food/snack served; some IQIS related material presented
4:15-4:35 Renate Scheidler�presentation
Classical Cryptographic Key Agreement Via Low Genus Curves
The celebrated 1976 Diffie-Hellman key agreement protocol allows two parties to securely establish a common secret cryptographic key across an insecure communication channel. Since then, a variety of structures have been proposed to serve as the underlying key space for this protocol. Among these, elliptic and genus 2 hyperelliptic curves are the most efficient and classically the most secure ... until quantum computers become a reality, in which case all discrete logarithm based public key cryptosystems will be completely broken. I will give a whirlwind tour of the arithmetic on such curves, explain how and why the genus 2 setting represents an attractive alternative to the much more widely used elliptic curves, and touch upon my own research interests in this area.
Looking forward to seeing you all!
The princess and the EPR pair
Aram Harrow [University of Washington]
17 August 2011 - abstract -

Abstract:
In quantum information, entanglement has often been viewed as a resource. But in this talk, I will look at (pure bipartite) entanglement
through the lens of superselection rules. The idea is that it requires quantum communication not only to create entanglement, but also to destroy it in a way that doesn't leak information to the environment. As a result, when communication is scarce, superpositions of different numbers of EPR pairs can be difficult to obtain. This constraint is not a strict superselection rule, but rather an approximate version that gives rigorous bounds on achievable fidelities. After describing the general phenomenon, I will show how it relates to communication complexity, information theory and fairy tales about princesses. This talk is based on 0803.3066, 0909.1557, 0912.5537 and other unpublished work.
Spectral Manipulation of Optical Pulses Using the Gradient Echo Memory Scheme
Ben Sparkes [Australian National University]
15 August 2011 - abstract -

Abstract:
The burgeoning fields of quantum computing and quantum key distribution have created a demand for a quantum memory. The gradient echo memory (GEM) is one such scheme that can boast efficiencies approaching unity. Here we investigate the ability of GEM to spectrally manipulate light pulses stored in the memory. Spectral manipulation is important for pulse compression sideband extraction, and matching of pulse spectra to resonant and spectroscopic systems, as well as the potential to increase qubit rates in quantum communications networks. We present both theoretical and experimental results demonstrating the ability to shift the frequency, as well as spectrally compress or expand a pulse. Also the ability of GEM to recall different frequency components of a pulse at different times, and interfere two initially time separated pulses that are stored in the memory, are shown.
Is it entangled? A quasi-polynomial time algorithm for the quantum separability problem.
Fernando Brand�o [Universidade Federal de Minas Gerais, Belo Horizonte, Brazil]
Co-sponsored by: PIMS CRG MQI Seminar Series
20 July 2011 - abstract -

Abstract:
Quantum mechanics predicts the existence of correlations between two quantum systems which cannot be described merely by shared randomness. Such correlations, termed entanglement, have been analysed from a fundamental perspective since the beginning of quantum theory and, more recently, as a resource for quantum information-theoretic tasks, such as quantum key distribution and teleportation. A fundamental problem in entanglement theory is the following: given the description of a quantum system of two parties as a density matrix, how can we decide if the state is entangled or separable? In this talk I will discuss the fastest known algorithm for solving this problem. The algorithm works by considering a sequence of SDP (semidefinite programming) relaxations to the problem, which are shown to converge quickly to the true solution.
Finally I will discuss a few�other applications of the techniques developed to quantum information
theory and quantum complexity theory. The talk is based on joint work with Matthias Christandl and Jon Yard (STOC 2011 and Commun. Math. Phys. '11)
A Combinatorial Perspective of Error Analysis in Molecular Dynamics
Reginald Paul [University of Calgary]
22 June 2011 - abstract -

Abstract:
In this talk I will compare two approaches that have evolved for the computation of general time displacement operators:
(1) Based on the Taylor expansion (moment expansion) and re-summation of the terms in an approximate fashion leading to such methods as truncated continued fractions.
(2) The more modern approach based on molecular dynamics for which I will derive an analytical form (Analytical Molecular Dynamics or AMD) that can be used to calculate the implicit moments for comparison with the results in (1).
Using very simple combinatorics I will derive a formula that will show the precise manner in which a finite step approximation based on AMD converges to the exact result. I will also show that the method commonly used in numerical simulations (Conventional Molecular Dynamics) lacks this convergence and, in fact, diverges. I will conclude that by using modern computational methods such as Mathematica it is possible to use the moment expansion methods to get better results than MD.
High transmission-loss and classical-quantum multiplexing QKD�enabled with short wavelength photons
Thomas Jennewein [University of Waterloo]
20 June 2011 - abstract -

Abstract:
I will present recent results on quantum key distribution (QKD) using short optical�wavelengths (532nm, 810 nm). These wavelengths offer unique applications�such as operation with ultra-high channel losses of 60dB, and entanglement based QKD over existing IT�infrastructure by multiplexing classical and quantum signals on the same optical fibre.
Measuring small longitudinal phase shifts: weak measurements or standard interferometry?
Nicolas Brunner [University of Bristol]
17 May 2011 - abstract -

Abstract:
Recently, weak measurements were used to measure small effects that are transverse to the propagation direction of a light beam. Here we address the question whether weak measurements are also useful for measuring small longitudinal phase shifts. We show that standard interferometry greatly outperforms weak measurements in a scenario involving a purely real weak value. However, we also present an interferometric scheme based on a purely imaginary weak value, combined with a frequency-domain analysis, which may have potential to outperform standard interferometry by several
orders of magnitude.

After this (short) talk, I will also present results on device-independent tests of classical and quantum dimensions.
Violation of Bell inequalities with photon counting and homodyne measurements
Daniel Cavalcanti [National University of Singapore]
16 May 2011 - abstract -

Abstract:
When separated measurements on entangled quantum systems are performed, the theory predicts correlations that cannot be explained by any classical mechanism: communication is excluded because the signal should travel faster than light; pre-established agreement is excluded because Bell inequalities are violated. All optical demonstrations of such violations have involved discrete degrees of freedom and are plagued by the detection-efficiency loophole. A promising alternative is to use continuous variables combined with highly efficient homodyne measurements. However, all the schemes proposed so far use states or measurements that are extremely difficult to achieve, or produce very weak violations. In this talk I will present a simple method to generate large violations for feasible states using both photon counting and homodyne detections. The present scheme can be used to obtain nonlocality from easy-to-prepare Gaussian states (e.g. two-mode squeezed state) and requires efficiencies comparable to the best tests involving discrete variables.
Zero temperature quantum dissipation using a SQUID-tunable boundary
Tim Duty [University of New South Wales]
16 May 2011 - abstract -

Abstract:
The strong nonlinearity provided by superconducting Josephson tunnel junctions can be used in experiments for parametric down conversion of microwave fields. This has many potential uses for nanoscale engineered quantum systems, such as quantum-limited amplification, generation of non-classical microwave radiation, and the possibility of implementing quantum feedback control for solid-state quantum systems. In this talk, I describe two sets of experiments where the parametric driving is implemented using a superconducting quantum interference device (SQUID). The SQUID is integrated into a on-chip microwave transmission line, and thereby acts as a tunable boundary condition for microwave fields. In the first set of experiments, we investigate the quantum dynamics of a tunable coplanar cavity, which we model as a parametric oscillator with a quartic nonlinearity. When� driven above threshold, the oscillator exhibits bistability, and we observe a novel type of�quantum tunneling that we call "quantum activation". In the second set of experiments, we
investigate the dynamical Casimir effect (DCE) in a broadband, open 1D transmission line, where we observe two-mode squeezing of the emitted radiation.
On measuring dangling-bond charge-qubit dynamics
Zahra Shaterzadeh Yazdi [IQIS, University of Calgary]
27 April 2011 - abstract -

Abstract:
We showed that charge qubits formed from two silicon-surface dangling bonds (DBs) sharing one excess charge should overcome the high-decoherence drawbacks of larger-scale quantum-dot charge qubits. However, decoherence of this charge qubit is speculative as the dynamics has not yet been measured. Here we propose using an atomic force microscope to characterize the fast tunneling rate and decoherence of the charge qubit. In our scheme the dynamics are studied by observing frequency changes to an atomic force microscope cantilever. This cantilever is capacitively coupled to the dangling-bond pair, which is driven by a Terahertz electromagnetic field. Our scheme is analogous to studies of slow measurements to determine fast qubit dynamics.
An Efficient Algorithm for Optimizing Adaptive Quantum Metrology Processes
Alexander Hentschel [IQIS, University of Calgary]
20 April 2011 - abstract -

Abstract:
Precise metrology is an important task with applications to measurements of time, displacements, and magnetic field strength. However, the `standard quantum limit' (SQL) restricts achievable precision, beyond which measurement must be treated on a quantum level. Feedback-based metrological techniques are promising for beating the SQL but devising the feedback procedures is complicated and often involves clever guesswork.

I present an automated technique, based on machine-learning that replaces guesswork by a logical, fully automatic, programmable routine.
I explain our method using the example of interferometric phase estimation. Our algorithm autonomously learns to perform phase estimation based on experimental trial runs, which can be either simulated or performed using a real world experiment. The algorithm does not require prior knowledge about the experiment and is effective even if the interferometric quantum channel is a black box. Our new technique is robust against loss and decoherence. Furthermore, our algorithm
learns to account for systematic experimental imperfections and random noise, thereby making time-consuming error modelling and extensive
calibration dispensable. We show that our method outperforms the best known adaptive scheme for interferometric phase estimation.
Putting Floquet theory to work: Topology of time dependent Hamiltonians
Netanel Lindner [California Institute of Technology]
Co-sponsored by: PIMS CRG MQI Seminar Series
16 March 2011 - abstract -

Abstract:
Topological phases of matter have captured our imagination over the past few years, with tantalizing properties such as robust
edge modes and exotic non-Abelian excitations, and potential applications ranging from semiconductor spintronics to topological
quantum computation. Despite recent advancements in the field, our ability to control topological transitions remains limited, and usually requires changing material or structure properties. We
show that a topological state can be induced in a semiconductor quantum well, initially in the trivial phase, by irradiation with microwave frequencies, without changing the well structure, closing the gap and crossing the phase transition. We show that the quasi-energy spectrum exhibits a single pair of helical edge
states. We discuss the necessary experimental parameters for our proposal. This proposal provides an example and a proof of principle of a new non-equilibrium topological state: a ``Floquet
topological insulator''.
Scaling Quadripartite Entanglement in the Optical Frequency Comb
Matthew Pysher [University of Virginia]
10 March 2011 - abstract -

Abstract:
Scalability and coherence are two essential requirements for the experimental implementation of quantum information and quantum
computing. In this talk, I will address the former and report the simultaneous generation of 15 quadripartite continuous-variable cluster states over 60 cavity modes in the optical frequency comb of a single optical parametric oscillator. This result paves the way for the realization of large-scale entangled states for quantum computing, as a slightly more sophisticated version of this experimental method
has theoretically shown the ability to produce arbitrarily large square-grid cluster states suitable for universal one-way quantum computing.
Quantum Theory Cannot be Extended
Roger Colbeck [Perimeter Institute]
24 February 2011 - abstract -

Abstract:
According to quantum theory, measurements generate random outcomes, in stark contrast with classical mechanics. This raises the important question of whether there could exist an extension of the theory which removes this indeterminism, as famously suspected by Einstein, Podolsky and Rosen. Although Bell showed this to be impossible, existing results do not imply that the current theory is maximally informative. Could it be that hidden variables allow us to make more accurate predictions of the outcomes? In this talk, I will focus on this question and present a new result that, under the assumption that measurements can be chosen freely, the answer is negative: no extension of quantum theory can give more information about the outcomes of future measurements than quantum theory itself.
A fully tunable microcavity
Russell J Barbour [University of Oregon]
23 February 2011 - abstract -

Abstract:
Optical microcavities that combine high Q-factors with a small mode volume play a vital role in modifying the interaction between light and matter. Several interesting phenomena arise when an emitter is introduced into such a cavity. These include enhancement or suppression of the spontaneous emission rate (weak coupling) and normal mode splitting (strong coupling).

The majority of successful microcavity experiments have been performed on self-assembled quantum dots. For quantum dots the work-horse cavity geometries are micropillars, photonic crystals and whispering gallery devices. However these devices lack in situ spatial tuning and offer only very limited spectral tuning.

In this seminar I will present the development of a miniaturized, fully tunable Fabry-Perot microcavity for quantum dot experiments. We have demonstrated unprecedented in situ control over a single quantum dot within the cavity, spatially positioning the dot at the exact anti-node of the cavity electric field. Spectral and spatial tuning of a single dot Purcell effect has been demonstrated.

Finally, I will talk briefly about my work towards coupling NV- centers in a diamond nanopillar to a deformed silica microsphere at cryogenic temperature.
Applications of a family of norms in entanglement theory
Nathaniel Johnston [University of Guelph]
9 February 2011 - abstract -

Abstract:
I will introduce a family of operator norms based on the Schmidt decomposition theorem and focus on their applications in quantum information theory. We will discuss two problems in particular: the
existence problem for non-positive partial transpose bound entangled states and the problem of computing or estimating the minimum gate
fidelity of a quantum channel. We will discuss some techniques for computing the norms and how they apply in the special cases of NPPT bound entanglement and minimum gate fidelity.
Some results concerning separable states in QIT
Shmuel Friedland [University of Illinois at Chicago]
Co-sponsored by: MITACS QIP Seminar Series
4 February 2011 - abstract -

Abstract:
The most basic notions in QIT are separable and entangled states. One of the most fundamental questions in this field is to recognize if a given state is separable or entangled. We will discuss some recent results related to this question.
The discrete time quantum walk: Universality, transport and searching
Neil Lovett [University of Leeds]
Co-sponsored by: MITACS QIP Seminar Series
19 January 2011 - abstract -

Abstract:
Quantum walks have played an important role in the development of new quantum algorithms and also in other applications. In this talk, we show how the discrete time quantum walk can be shown to be universal for quantum computation. This work highlights structures on which perfect state transfer can be achieved with the quantum walk, an important property for both quantum communication and computing. High fidelity transport is also important in other fields including quantum biology. For example, charge transfer in photosynthetic bacteria can essentially be viewed as a quantum walk with
decoherence. Finally, we move on to the application of the discrete time quantum walk to searching. Previous work has highlighted a dependence on the dimension of the dataset to be searched. Here, we investigate a secondary
dependence on the underlying connectivity of the structure. We consider regular lattices, showing how the algorithmic efficiency is increased by additional connectivity. In addition, we study the effect of disorder on the algorithm using randomly generated percolation lattices. We show this disorder reduces, and eventually removes, the quantum speed up provided by the quantum algorithm.

2010

A family of norms with applications in entanglement theory
David Kribs [University of Guelph]
Co-sponsored by: PIMS CRG MQI Seminar Series
1 December 2010 - abstract -

Abstract:
I will discuss recent work with Nathaniel Johnston in which we consider a family of operator norms that quantify the degree of entanglement in quantum states. The norms are defined by the Schmidt decomposition theorem for quantum states, and they can be used to tackle two fundamental problems in quantum information theory: the classification problem for k-positive linear maps and entanglement witnesses, and the existence problem for non-positive partial transpose bound entangled states. Time dependent, I'll discuss some properties of the norms and their applications.
A generalization of Noether's theorem and the information-theoretic approach to the study of symmetric dynamics
Iman Marvian [Perimeter Institute]
28 October 2010 - abstract -

Abstract:
Information theory provides a novel approach to study of the consequences of symmetry of dynamics which goes far beyond the traditional conservation laws and Noether's theorem. The conservation laws are not applicable to the dissipative and open systems. In fact, as we will show, even in the case of closed system dynamics if the state of system is not pure the conservation laws do not capture all the consequences of symmetry. Using information theoretic approach to this problem we introduce new quantities called asymmetry monotones, that if the system is closed �they are constant of motion �and otherwise, if the system is open, they are always non-increasing. We also explain how different results in quantum information theory can have non-trivial consequences about the symmetric dynamics of quantum systems.�
Specker's parable of the overprotective seer: Implications for Contextuality, Nonlocality and Complementarity
Rob Spekkens [Perimeter Institute]
Co-sponsored by: MITACS QIP Seminar Series
27 October 2010 - abstract -

Abstract:
I revisit an example of stronger-than-quantum correlations that was discovered by Ernst Specker in 1960. The example was introduced as a
parable wherein an over-protective seer sets a simple prediction task to his daughter's suitors. The challenge cannot be met because the seer asks the suitors for a noncontextual assignment of values but measures a system for which the statistics are inconsistent with such an
assignment. I will show how by generalizing these sorts of correlations, one is led naturally to some well-known proofs of nonlocality and contextuality, and to some new ones. Specker's parable involves a kind of complementarity that does not arise in quantum theory - three measurements that can be implemented jointly pairwise but not triplewise -- and therefore prompts the question of what sorts of foundational principles might rule out this kind of complementarity.

Joint work with Howard Wiseman and Yeong-Cherng Liang.
Optimal quantum learning of an unknown unitary transformation and multiround reference frame alignment
Giulio Chiribella [Perimeter Institute]
26 October 2010 - abstract -

Abstract:
Quantum combs and testers entail a new paradigm of quantum information processing where the input of transformations and measurements are quantum
channels rather then states. In this talk, I will present two applications of this paradigm. The first application is the optimal automated learning of an unknown qubit unitary from a finite training set of N examples. The examples
are first exploited in an optimal storing network, whose output state is then sent to a retrieving machine that optimally reproduces the unknown unitary M times. The second application is the optimal alignment of reference frames with multiple rounds of quantum and classical communication. In this case, quantum combs and testers provide a simple proof that the maximum precision of reference frame alignment only depends on the total number of exchanged qubits,
and that a single round of forward quantum communication is sufficient to achieve it.
Control and Error Prevention in Quantum Computing Devices
Mark Byrd [Southern Illinois University]
Co-sponsored by: MITACS QIP Seminar Series
20 October 2010 - abstract -

Abstract:
Errors are the greatest obstacle to building a reliable and scalable quantum computing device. Several advances have been made on the theoretical front, but the question is whether or not they are
practical. In this talk I will provide a basic introduction to the theoretical constructs before discussing what appears to be practical. This includes previous work for preventing errors in solid-state quantum computing devices, recent work to extend the universal quantum control methods of decoherence-free/noiseless subsystems, and the development of new methods for practical modelling of quantum systems.
Error Estimates For The Quantum Adiabatic Approximation
Nathan Wiebe [IQIS, University of Calgary]
6 October 2010 - abstract -

Abstract:
The adiabatic approximation is frequently used in quantum sciences to approximate the time-evolution of quantum systems that are governed by a slowly varying time-dependent Hamiltonian. Despite the ubiquity of the approximation, it was shown in 2004 by Peter Marzlin and Barry Sanders that the criterion that is most commonly used for determining when the approximation is valid can fail for certain Hamiltonians. We address
these issues by presenting an intuitive and elementary proof of the adiabatic approximation that is based on path integrals. Furthermore, we
provide the tightest upper and lower bounds on the error in the adiabatic approximation that are currently known, and show that the bounds are
asymptotically tight for many Hamiltonians. Finally, we use these bounds to show that the Marzlin-Sanders counterexample Hamiltonian is marginally pathological in that if its second time-derivative were slightly diminished then the Hamiltonian would no longer be a counterexample. This work is collaborative work done with Donny Cheung and Peter Hoyer.
Coherent control of quantum interference in atomic systems
Ali Kamli [University of Jazan , Saudi Arabia]
5 October 2010 - abstract -

Abstract:
We review the basic ideas of quantum interference (QI) in three level V-type atomic systems due to spontaneous emission from upper levels to the third ground level. We discuss how to manipulate QI by controlling the amplitude and the phase of control fields. In the later part of the talk we study QI inside a cavity and show how QI is further controlled using various cavity parameters.
Quantum Hindsight: Quantum Parameter Estimation Using Smoothing
Elanor Huntington [University of New South Wales]
29 September 2010 - abstract -

Abstract:
Quantum parameter estimation has many applications, from gravitational wave detection to quantum key distribution. The most commonly used technique for this type of estimation is quantum filtering, using only past observations. We present the first experimental demonstration of quantum smoothing, a time symmetric technique that uses past and future observations, for quantum parameter estimation. We consider both adaptive and nonadaptive quantum smoothing, and show that both are better than their filtered counterparts. For the problem of estimating a stochastically varying phase shift on a coherent beam, our theory predicts that adaptive quantum smoothing (the best scheme) gives an estimate with a mean-square error up to 2-root-2 times smaller than nonadaptive filtering (the standard quantum limit). The experimentally measured improvement is 2.24.
Measuring entanglement
Nolan Wallach [University of California, San Diego]
18 August 2010 - abstract -

Abstract:
The physics literature in the last 10 years contains an immense number of papers related to multi-particle entanglement involving some very
sophisticated mathematics. In this lecture we will survey some of this work that centers on geometric invariant theory. Most of the concrete work has been done for at most 4 qubits. There are several reasons for this. One is the combinatorial explosion which we will explain and another is that for 2,3 or 4 qubits SLOCC is related to deep properties of SO(4), SO(8) and F_4.
Topological fault tolerant quantum computation with very high threshold for loss errors
Sean Barrett [Imperial College, London]
17 August 2010 - abstract -

Abstract:
Many proposals for fault tolerant quantum computation (FTQC) suffer detectable loss processes. Here we show that topological FTQC schemes, which are known to have high error thresholds, are also extremely robust against losses. We demonstrate that these schemes tolerate loss rates up to 24.9%, determined by bond percolation on a cubic lattice. Our numerical results show that these schemes retain good performance when loss and computational errors are simultaneously present.
Controlled generation of single photons in a cavity QED system
Christian N�lleke [Max Planck Institute of Quantum Optics, Garching]
Co-sponsored by: University of Calgary OSA student chapter
21 July 2010 - abstract -

Abstract:
Quantum Information Processing (QIP) in quantum networks relies on the coherent exchange of information between light and matter. Neutral atoms trapped in high-finesse optical cavities are ideal candidates for such light-matter interfaces and can also offer a platform which would enable QIP with linear optics.

We generate single-photon streams via a vacuum-stimulated Raman adiabatic passage, using a single Rubidium atom trapped in a cavity. In comparison to other sources, the coherence of the production process allows us to have full control over the temporal shape, frequency, polarization and phase of the photons. A fundamental prerequisite for the experimental realization of applications in QIP is a high efficient photon production process.

A careful tuning of all experimental parameters has now allowed us to boost the photon generation efficiency to 60%, much higher than in previous experiments. Moreover, the duty cycle of the experimental sequence is now close to unity, owing to atom trapping times of more than one minute on average. With such an optimized setup, it is now possible to run the system in a quasi-permanent operation.

We report on the current status of the experiment and present prospects for highly efficient single-photon servers as quantum memories.
Compressed Tomography of Quantum Dynamical Systems
Alireza Shabani [Princeton University]
30 June 2010 - abstract -

Abstract:
A fundamental problem in characterization of complex quantum systems is the exponential growth in the required physical resources with the size
of system. We develop an efficient method for complete estimation of an unknown quantum process/Hamiltonian with a polynomial number of experimental configurations via employing techniques known as compressed sensing. We demonstrate that by O(s \log d) random local
preparations and measurements settings one can fully identify a quantum process/Hamiltonian for a d-dimensional system, if it is known to be nearly s-sparse in a basis. We present the first experimental implementation of this method for two- and four-photon quantum optical systems with a significant reduction in physical resources compare to known tomography techniques. Moreover, we demonstrate robustness of this technique by performing efficient high-fidelity estimation of
two-qubit photonic phase gates under various decoherence strengths.
Making and breaking entanglement-based QKD
Antia Lamas Linares [National University of Singapore]
18 June 2010 - abstract -

Abstract:
I will describe the basic QKD platform used in Singapore and a number of the experiments that have been performed on top of that. Our system is entanglement-based and uses the polarization degree of freedom for encoding. It is a small, robust platform that is easily adaptable and we have used it to perform field implementations of BBM92, device independent QKD and daylight free space QKD. Finally, I will discuss recent results on system vulnerabilities. A complete key recovery by a malicious eavesdropper using the "faked states" attack was demonstrated in the field, and raises some questions on the security of the physical devices used in quantum cryptography.
Comparison of experiments on general quantum systems - a Quantum Blackwell Theorem
Francesco Buscemi [Nagoya University, Japan]
25 May 2010 - abstract -

Abstract:
Between 1949 and 1953, Blackwell proved a theorem, which is now a famous result in classical statistics, formalizing the idea that one experiment is more informative than another if and only if the latter can be simulated by suitably processing the outcomes of the former. A quantum analogue of Blackwell Theorem was proposed in [Shmaya, J.Math.Phys. 38, 9717-9727 (2005)]. Shmaya's comparison method, however, always and necessarily requires the presence of an extra entangled resource, even if the two experiments to be compared are purely classical. This makes Blackwell Theorem, which is a classical result,
independent from Shmaya's approach, which is, instead, purely quantum. Here, by introducing the notion of state space processing for general convex sets of states, we are able to bridge such a gap and treat classical and quantum experiments comparison on an equal footing. As an interesting by-product, we show that it is in fact possible to re-derive all of Shmaya's results without ever resorting to any extra entangled resource.
On some problems and applications of tensors
Shmuel Friedland [University of Illinois, Chicago]
11 May 2010 - abstract -

Abstract:
In recent years the study of tensors, i.e. multiarrays, became a topic of an extensive research in applied and pure mathematics. In this talk we discuss a number of problems in: quantum information theory, theoretical computer science, algebraic geometry and algebraic statistics.
Hamiltonian simulation via quantum walks
Dominic Berry [Institute for Quantum Computing, University of Waterloo]
28 April 2010 - abstract -

Abstract:
Hamiltonian simulation can be used to simulate physical systems, and is also the basis for many new quantum algorithms. I present methods to
simulate black-box Hamiltonians with fixed error using a number of queries that scales as O(||H||tD), where D is the maximum number of
nonzero elements in any column, t is the evolution time and ||H|| is the spectral norm of the Hamiltonian. In contrast, previous methods had
complexity scaling as D^4, and slightly superlinear scaling in ||H||t.
Alternatively, for D>||H||t the scaling can be improved to approximately O([||H||t]^{4/3}D^{2/3}). Numerical testing indicates that in almost all cases the scaling can be further improved to approximately O([||H||t]^{3/2}D^{1/2}). One application of this is to implementation of black-box unitaries with O(N^{1/2}) queries. In contrast, standard methods take at least N^2 elementary gates. This could be used to more efficiently implement unitaries in cases where the matrix elements can be efficiently calculated.
Simulating Hamiltonian dynamics
Andrew Childs [Institute for Quantum Computing, University of Waterloo]
Co-sponsored by: MITACS QIP Seminar Series
10 March 2010 - abstract -

Abstract:
Hamiltonian simulation is a basic task in quantum computation, with applications both to simulating physical systems and implementing continuous-time quantum algorithms. I will describe two methods for sparse Hamiltonian simulation, one based on star decompositions and another based on discrete-time quantum walk. Both methods are faster than previously known approaches; which of the two is preferred depends on the desired accuracy of the simulation. I will also describe a technique for simulating non-sparse Hamiltonians, and show that no such method can run in time poly(||Ht||) in general.

Parts of this talk are based on joint work with Dominic Berry and with Robin Kothari.
Matrix Product States and Quantum Phase Transition
Khabat Heshami [IQIS, University of Calgary]
24 February 2010 - abstract -

Abstract:
The study of strongly correlated systems attracts much attention from condensed matter physicists since quantum fluctuations introduce different phases with interesting physical properties. Several numerical and analytical approaches have been developed to investigate properties of low lying states. However, there is no specific framework in place to deal with the challenging problem of Quantum Phase Transition (QPT). We propose a method to detect some of QPTs based on a matrix product representation of the ground state of strongly correlated systems with local Hamiltonians. As a confirmation of our proposed method, we show that our analytical results compare favorably with numerical studies of XXZ spin-one chain with uniaxial single-ion-type anisotropy.
Strong superadditivity and monogamy of the Renyi measure of entanglement
Marcos C�sar de Oliveira [Universidade Estadual de Campinas]
Co-sponsored by: MITACS QIP Seminar Series
10 February 2010 - abstract -

Abstract:
Employing quantum R�nyi α-entropies as a measure of entanglement, we numerically find violation of the strong superadditivity inequality for a system composed of four qubits and α>1. This violation gets smaller as α goes to 1 and vanishes for α=1.
For α=2, we also show that the R�nyi measure satisfies the standard monogamy of entanglement and that the violation of the strong superadditivity occurs very rarely but always simultaneous to the violation of a high order monogamy inequality. We thus conjecture that
strong superadditivity violation of this entanglement measure is necessary and sufficient for the high order monogamy relation violation.
Optical implementation of a new factorization algorithm
Vincenzo Tamma [University of Maryland Baltimore County]
3 February 2010 - abstract -

Abstract:
We construct an analogue computer based on wave interference to encode the hyperbolic function f(ξ)= 1-ξ into a continuous exponential sum. The resulting interferogram when scaled appropriately allows us to factor not only a single but a wide range of numbers. We implement this new algorithm exploiting polychromatic optical interference in a multi-path interferometer and factor seven digit numbers.
Efficient, solid-state quantum memory for light
Morgan Hedges [Laser Physics Centre, Australian National University]
2 February 2010 - abstract -

Abstract:
We report on the storage and retrieval of coherent light pulses using rare-earth ions doped into a crystal and a gradient-echo technique. Using this system we find efficiencies as high as 70%. By further performing homodyne tomography, we are able to confirm its operation better than the classical and no-cloning limits.

2009

Quantum computational phases of matter
Stephen Bartlett [University of Sydney]
Co-sponsored by: MITACS QIP Seminar Series
25 November 2009 - abstract -

Abstract:
A recent breakthrough in quantum computing has been the realization that quantum computation can proceed solely through single-spin measurements on
an appropriate quantum state. One exciting prospect is that the ground or low-temperature thermal state of an interacting quantum many-body system can serve as such a resource state for quantum computation. The system would simply need to be cooled sufficiently and then subjected to local measurements. It would be unfortunate, however, if the usefulness of a ground or low-temperature thermal state for quantum computation was critically dependent on the details of the system's Hamiltonian. A much more powerful result would be the existence of a robust ordered phase which is characterized by the ability to perform measurement-based quantum computation. I'll discuss some recent results on the existence of such a quantum computational phase of matter, including a specific realistic model in a spin-1 chain.

Joint work with Gavin Brennen, Akimasa Miyake, and Joseph Renes.
A new uncertainty principle near the Planck scale and its implications
Saurya Das [University of Lethbridge]
18 November 2009 - abstract -

Abstract:
Most approaches to Quantum Gravity and Black Hole Physics suggest some modification of the Heisenberg Uncertainty Principle near the Planck
energy scale to a so-called Generalized Uncertainty Principle (GUP). We propose a GUP consistent with all such approaches, and show that it predicts a minimum observable length and a maximum observable momentum. We also show that it gives rise to a new term in all quantum mechanical Hamiltonians, which can have measurable signatures in various low energy systems, such as in condensed matter and atomic physics. Further, it also indicates a breakdown of the continuum nature of spacetime near the Planck scale, giving way to an intrinsically discrete structure. We ask whether such discreteness can have experimental signatures at observable length scales.
Ultra Fast Quantum State Tomography
Steve Flammia [Perimeter Institute, Waterloo]
Co-sponsored by: MITACS QIP Seminar Series
4 November 2009 - abstract -

Abstract:
Everybody hates tomography. And with good reason! Experimentalists hate it because it is inefficient and difficult. Theorists hate it because it isn't
very "quantum." But because of our current lack of meso-scale quantum computers capable of convincingly performing non-classical calculations, tomography seems like a necessary evil. In this talk, I will attempt to banish quantum state tomography to the Hell of Lost Paradigms where it belongs. I hope to achieve this by introducing several methods for learning
quantum states more efficiently, in some cases exponentially so. The first method runs in polynomial time and outputs a polynomial-sized classical approximation of the state (in matrix product state form), together with a rigorous bound on the fidelity. The second result takes advantage of the fact that most interesting states are close to pure states to get a quadratic speedup using ideas from compressed sensing. I'll also show simulations of this second method that demonstrate how well it works in practical situations. Both of these results are heralded, and require no a priori assumptions about the state.

This is joint work with S. Bartlett, D. Gross, R. Somma (first result), and D. Gross, Y.-K. Liu, S. Becker, J. Eisert, (second result; arXiv:0909:3304).
Electron spin qubits in quantum dots: a micro-magnet approach
Michel Pioro-Ladri�re [Universit� de Sherbrooke]
26 October 2009 - abstract -

Abstract:
Electron spins isolated in quantum dots are promising candidates for the physical implementation of quantum information processing in the solid-state. After introducing how quantum information can be stored and manipulated with electron spins in modern quantum dots, I will review the recent experimental successes and the difficulties that have been encountered. Building on these results, I will demonstrate how the integration of micron-size ferromagnets can help in solving the problem of addressability and at the same time in enabling scalable, all-electrical, one-qubit gates.
A frameness measure for mixed states
Borzumehr Toloui Semnani [IQIS, University of Calgary]
21 October 2009 - abstract -

Abstract:
Almost all states and operations in the lab involve some degree of mixedness, so it is necessary to extend the results of the newly developed reference frame (RF) resource theories to include mixed states. We will go over different ways of extending measures of frameness to mixed states, and point out some of the differences between entanglement and quantum RFs that need to be taken into account for defining "frameness of formation".

The frameness of formation denotes the average resource cost of generating a mixed state. The cost is measured in terms of standard resource states, called refbits, that are chosen as units of frameness. We will produce explicit results for a qubit's frameness of formation under the group U(1) associated with phases. In order to determine the exact value of this frameness measure, we develop a novel technique that generalizes Wootter's idea for entanglement of formation to RF resource theories. We introduce "concurrence of frameness" as a generalization of the concurrence measure to quantum RFs, and determine the concurrence of a resource state explicitly. Finally, the cost of preparing a resource is expressed as a simple function of this concurrence.
Remote state preparation with classical versus quantum resources
Nathan Killoran [Institute for Quantum Computing, University of Waterloo]
6 October 2009 - abstract -

Abstract:
Remote state preparation (RSP) is the act of preparing a quantum state at a remote location without actually transmitting the state itself.
Using at most two classical bits and a single shared maximally entangled state, one can in theory remotely prepare any qubit state
with certainty and with perfect fidelity. However, in any experimental implementation the average fidelity between the target and output
states cannot be perfect. In order for an RSP experiment to demonstrate genuine quantum advantages, it must surpass the optimal threshold of a comparable classical protocol. In this talk, I will outline how to find the maximum fidelity achievable by RSP protocols lacking shared entanglement. From this, I will propose several experimental benchmarks that can be used to verify genuine quantum behaviour in any RSP protocol. Finally, I will report on a recent RSP
experiment and compare our experimental results with the proposed benchmarks.
On-chip cavity QED: atoms, defects, and nanostructures (Department of Physics and Astronomy Research Seminar)
Paul Barclay [Hewlett-Packard Labs]
1 October 2009 - abstract -

Abstract:
Color centers, formed by defects or impurities in crystalline materials such as silicon and diamond, are promising solid state "atom-like" emitters. Recently, the diamond nitrogen vacancy (NV) center has been shown to possess long lived, optically addressable, electron and nuclear spins which may be useful as qubits for quantum information processing. An outstanding challenge in using NVs in quantum information processing applications is efficient and scalable optical coupling. I will discuss recent studies of optical coupling between NVs and a variety of nanophotonic structures, including dielectric and bulk diamond microcavities. These devices allow the modification of the spontaneous emission properties NVs, and will enable efficient generation of single photon pulses entangled with NV spins.
Quantum computation with controlled-path and merging gate
Bing He [IQIS, University of Calgary]
30 September 2009 - abstract -

Abstract:
We present a simple architecture for deterministic quantum circuits operating on single photon
qubits. Few resources are necessary to implement two elementary gates and can be recycled for computing with large numbers of qubits. The deterministic realization of some key multi-qubit gates, such as the Fredkin and Toffoli gate, is greatly simplified in this approach.
Geometrizing quantum adiabatic computation
Ali Rezakhani [University of Southern California]
23 September 2009 - abstract -

Abstract:
A time-optimal approach to adiabatic quantum computation (AQC) will be formulated. The corresponding natural Riemannian metric is also derived, through which AQC can be understood as the problem of finding a geodesic on the manifold of control parameters. This geometrization of AQC is demonstrated through some examples, where I show that it leads to improved performance of AQC, and sheds light on the roles of entanglement and curvature of the control manifold in algorithmic performance.
Alignment of cartesian reference frames and platonic solids
Piotr Kolenderski [Nicolaus Copernicus University, Poland]
16 September 2009 - abstract -

Abstract:
We discuss the problem of Cartesian reference frame alignment in case when there is initial information about the orientation. We show that the optimal states of N qubits correspond to platonic solids in Majorana representation.
Quantum entanglement in photosynthetic light harvesting
Mohan Sarovar [University of California, Berkeley]
10 September 2009 - abstract -

Abstract:
Identification of non-trivial quantum mechanical effects in the functioning of biological systems has been a long-standing and elusive goal in the fields of physics, chemistry and biology. Recent progress in control and measurement technologies, especially in the optical spectroscopy domain, have made possible the identification of such effects.

I examine light harvesting components of photosynthetic organisms -- complex, coupled, many-body quantum systems -- in which electronic
coherence has recently been shown to survive for relatively long time scales despite the effects of their noisy environments. By constructing useful measures of entanglement for such systems, and
using an accurate model of energy transfer dynamics in the presence of noise, I demonstrate the existence of quantum entanglement in a
commonly studied light harvesting complex. The lifetimes and temperature dependency of entanglement are examined in detail. This
study constitutes the first rigorous quantification of entanglement in a biological system. Finally, I will discuss the practical utilization of entanglement in densely packed molecular aggregates such as light harvesting complexes.

Joint work with: A. Ishizaki, G. R. Fleming, and K. B. Whaley
Based on: arXiv:0905.3787 [quant-ph]
The complexity of implementing NxN black-box unitaries is O(N^{3/4})
Dominic Berry [Institute for Quantum Computing, University of Waterloo]
9 September 2009 - abstract -

Abstract:
Standard methods for implementing arbitrary $N\times N$ unitaries require $\Omega(N2)$ gates. We consider a black box that outputs the matrix elements of the unitary, and show that the unitary may be performed with fidelity $1-\xi$ using $O(N^{3/4}/\xi^{1/2})$ black-box calls. This may be achieved by using a quantum walk, where each step of the quantum walk is performed using amplitude amplification. Except for pathological cases, higher-order integrators may be used to improve the scaling to $O((N/\xi)^{1/2+\epsilon})$ black-box calls, for any $\epsilon>0$. In comparison, state preparation via amplitude amplification can be performed with $O(N^{1/2})$ black-box calls; almost the same scaling in $N$.
Resource theory of quantum reference frames
Iman Marvian [Institute for Quantum Computing, University of Waterloo]
26 August 2009 - abstract -

Abstract:
For every restriction on operations there is a resource theory, determining how states may be manipulated and used to circumvent the restriction. In the resource theory of quantum reference frames we are restricted to use quantum operations which are invariant under the effect of a given group. This restriction may arise, for example, when two distant parties lack a shared reference frame. The states that circumvent it (the resources) are called quantum reference frames. We introduce a new framework for studying this resource theory. This method is based on representing states by their characteristic functions which are functions from the group to the complex numbers. Using this new method we can answer different interesting questions in the resource theory of quantum reference frames. In particular, in this talk I will use this method to solve the problem of asymptotic reversible transformation between resources. I will also discuss about other possible applications of this method.
Quantum Computing with Dangling Bond Pairs on a Si Surface
Zahra Shaterzadeh Yazdi [IQIS, University of Calgary]
19 August 2009 - abstract -

Abstract:
If, one day, a quantum computer is built, it would be able to efficiently solve some intractable computational problems such as factorizing large integers; this is something that would never be possible with today's classical computers. Despite all impressive progress that has been achieved in developing silicon quantum computing (QC) implementations for both spin and charge qubits, there are still serious obstacles remained for realizing such schemes where decoherence effects in charge qubit and read-out in spin qubit cases are at the heart of these challenges. A promising approach in overcoming the spin-qubit problem is to convert it to a charge qubit before doing the measurement. Thus, looking for a practical Si-based charge qubit is important not only as a quantum information carrier but also as an intercessor for spin-qubit measurement.

We propose a feasible charge qubit QC scheme but on a Si surface rather than in crystal bulk. In our scheme charge qubit is an excess electron shared between two nearby dangling bonds (DBs). A DB is a bond created by removing a hydrogen atom by means of a scanning tunneling microscope (STM) tip from the hydrogen-terminated Si(100)2x1 surface. Signature of coupled DBs for a distance between 4 to 15 angstroms has already been shown experimentally in the demonstration of a quantum cellular automata unit cell on Si(100)2x1 surface and the implementation of our scheme is in fact leveraged on this success. Our scheme has a couple of significant advantages over the other proposed bulksilicon QC schemes: long coherence time, and direct manipulation and measurement of qubits on the surface. In my talk, I will address DiVincenzo criteria and demonstrate how our proposed scheme fulfill these criteria.
Mathematical Optics at the National Laser Centre
Andrew Forbes and Stef Roux [CSIR National Laser Centre, South Africa]
10 August 2009 - abstract -

Abstract:
Our everyday experience of light is with the intensity of the field - how bright it is, or how much energy it carries - yet control and understanding of the phase of light opens doors to endless possibilities for new science in both the classical and quantum worlds. In this talk we will outline some research activities within the Mathematical Optics group at the South African National Laser Centre, and show how light may be tailored through phase into exhibiting interesting properties for various applications. In particular we will highlight the impact of optical vortices on the properties of strongly scintillated optical beams, and show how an understanding of the statistical behaviour of vortex fields may aid in the removal of such vortices.
The impact of classical electronics constraints on a solid-state logical qubit memory
Andrew Landahl [Sandia National Laboratories]
7 August 2009 - abstract -

Abstract:
I will describe a fault-tolerant memory for an error-corrected logical qubit based on silicon double quantum dot physical qubits. The design accounts for constraints imposed by supporting classical electronics. A significant consequence of the constraints is to add error-prone idle steps for the physical qubits. Even using a schedule with provably minimum idle time, for the noise model and choice of error-correction code, we find that these additional idles negate any benefits of error correction. Using additional qubit operations, we can greatly suppress idle-induced errors, making error correction
beneficial, provided the qubit operations achieve an error rate less than $2 \times 10^{-5}$. I will discuss other consequences of these constraints such as error-correction code choice and physical qubit operation speed. While th analysis is specific to this memory architecture, the methods developed are general enough to apply to other architectures as well.
How to maximize the information transfer via a quantum noisy channel?
Gershon Kurizki [Weizmann Institute of Science , Rehovot, Israel]
28 July 2009 - abstract -

Abstract:
We discuss a key concept in single - photon communications: quantum channel capacity, which measures information transfer in the presence of noise or decoherence and ways of enhancing
this capacity by a combination of an appropriate measurement basis, entanglement and dynamic control (pulse shaping). We next examine the implications of path-phase complementarity on the input-output mutual information in such scenarios.
New optical quantum logic gates and their application to quantum chemistry
Ben Lanyon [University of Queensland]
22 July 2009 - abstract -

Abstract:
I'll talk about some recent work done by our experimental quantum information group at the University of Queensland, Australia, where we are developing techniques for encoding, processing and measuring quantum information in photons. Firstly I'll present our recent implementation of two new quantum logic gates, which are the building blocks of a quantum computer. Then I'll talk about our early experimental step towards using a quantum computer to solve otherwise intractable physics problems - specifically, calculating the energy spectrum of molecules. I will assume no prior knowledge of optical quantum computing but some of quantum information.
Post-processing for quantum key distribution
Xiongfeng Ma [Institute for Quantum Computing, University of Waterloo]
30 April 2009 - abstract -

Abstract:
Quantum key distribution (QKD) promises unconditionally secure key generation between two distant parties by wisely exploiting properties of quantum mechanics. In QKD, experimental measurements on quantum states are transformed to a secret key and this has to be done in accordance with a security proof. Unfortunately, many theoretical proofs are not readily implementable in experiments and do not consider all practical issues. Therefore, in order to bridge this "practical gap", we integrate a few existing theoretical results together with new developments, in effect producing a simple and complete recipe for classical post-processing that one can follow to derive a secret key from the measurement outcomes in an actual QKD experiment. This integration is non-trivial and our consideration is both practical and comprehensive in the sense that we take into account the finiteness of the key length and consider the effects on security of several essential primitives (including authentication, error handling, and privacy amplification). Furthermore, we quantify the security of the final secret key that is universally composable. We show that the main contribution of the finite-size effect comes from phase error estimation.
Machine Learning for Adaptive Quantum Control and Measurement
Alexander Hentschel [IQIS, University of Calgary]
29 April 2009 - abstract -

Abstract:
For many applications, like atomic clocks or gravitational wave detection, it is essential to precisely ascertain an optical phase. The goal of quantum measurement is to get as close to the fundamental Heisenberg limit as possible.
I will present a method for designing measurement protocols that are closest to the Heisenberg limit. Our approach is based on a self-learning particle swarm algorithm that is trained on a simulated experiment to perform optimal phase estimation. Our algorithm learns solely based on training without any knowledge about the physical system. I will explain how this technique can be extended such that the machine learning algorithm can be trained on a real world experiment.
Distilling bipartite entanglement from multipartite states
Ben Fortescue [IQIS, University of Calgary]
1 April 2009 - abstract -

Abstract:
I will discuss some previous and current work on obtaining pure bipartite entanglement from pure multipartite entangled states through local operations and classical communication. The achievability of such transformations depends on both the amount of bipartite entanglement obtained and its distribution between parties. In the first part of the talk I will discuss a single-copy protocol that can, from certain multipartite states, produce substantially higher bipartite entanglement between post-selected compared to pre-selected parties. In the second part I will discuss what bounds are known and what can be achieved using this and other known protocols in the many-copy limit.
Entangled images: generation and delay with four-wave mixing
Alberto Marino [National Institute of Standards and Technology]
Co-sponsored by: University of Calgary Student Chapter of Optical Society of America
12 March 2009 - abstract -

Abstract:
I will present experimental studies that we have carried out on the
generation and delay of highly entangled beams of light, know as twin
beams. The quantum correlations present in twin beams have recently
generated great interest due to their applications in quantum
information, quantum imaging, and quantum computing. In the first
part of the talk I will show that non-degenerate four-wave mixing
(4WM) in a rubidium vapor cell is an excellent source of
continuous-variable (CV) entangled twin beams, with an
intensity-difference noise of less than 13% of the classical
shot-noise level. Unlike other systems that rely on the use of a
cavity, the system that we use can support a large number of spatial
modes. This leads to spatial quantum correlations and makes it
possible to produce CV entangled images. In the second part I will
show that, in addition to generating entangled twin beams, the 4WM
process in a vapor cell can act as a tunable delay line for CV
entanglement without significant degradation. This has allowed us to
delay entangled images.
Organic nanostructure formation on silicon surfaces: insights into tuning organic reactions and surface properties (Department of Chemistry Seminar)
Gino A. DiLabio [National Institute for Nanotechnology & National Research Council of Canada ]
30 January 2009 - abstract -

Abstract:
The modification of surfaces with organic molecules is one technique for incorporating new functionality into semiconductors. Organic molecules are attractive from this perspective because almost any property of a molecule can be altered through synthesis, and these properties can be used to �tune� the properties of a surface. Alternatively, the properties of a surface can be used to �tune� the kind of chemistry that can occur on a semiconductor surface. In this presentation, I describe how we use quantum mechanical simulations and scanning tunneling microscopy to understand processes leading to the formation of one- and two-dimensional organic nanostructures on silicon. Specific examples of molecular modification of surface properties and of surface modification of chemical mechanisms will be discussed.
A generalized Grothendieck inequality and entanglement in XOR games
Jop Briet [Centrum voor Wiskunde en Informatica (CWI), Amsterdam]
28 January 2009 - abstract -

Abstract:
Suppose Alice and Bob make local two-outcome measurements on a shared entangled state. For any d, we show that there are correlations that can only be reproduced if the local dimension is at least d. This resolves a conjecture of Brunner et al. [Phys. Rev. Lett. 100, 210503 (2008)] and establishes that the amount of entanglement required to maximally violate a Bell inequality must depend on the number of measurement settings, not just the number of measurement outcomes. We prove this result by establishing the first lower bounds on a new generalization of Grothendieck's constant.
Some linear and multilinear algebra aspects of quantum information theory
Shmuel Friedland [University of Illinois at Chicago]
7 January 2009 - abstract -

Abstract:
Some problems in Quantum Information Theory can be stated
simply in terms of completely positive, trace preserving
linear operators on the spaces of Hermitian matrices.
In this talk we show how basic tools of linear and multilinear
algebra can give estimates on the minimum entropy of quantum
channels.

Some of the results discussed in this talk can be found on

http://arxiv.org/abs/0809.0078

2008

Correlated spontaneous emission of a single photon from a uniformly excited cloud of N atoms
Marlan Scully [Texas A&M University and Princeton University]
12 December 2008 - abstract -

Abstract:
We study the correlated spontaneous emission from a dense spherical cloud of N atoms uniformly excited by absorption of a single photon. We find that the coupled atom-radiation system oscillates between the collective Dicke state (with no photons) and the atomic ground state (with one photon) with frequency Ω while decaying at a rate c/R; thus providing us with a new kind of cavity QED.
Quantum information processing with single photons and atomic ensembles
David Petrosyan [Institute of Electronic Structure & Laser (IESL), Foundation for Research and Technology - Hellas (FORTH)]
9 September 2008 - abstract -

Abstract:
Scalable and efficient quantum computation with photonic qubits requires deterministic sources of single photons, robust reversible photon storage, giant nonlinearities capable of entangling pairs of photons, and efficient photon detectors. I will discuss several related techniques, based on the coherent manipulation of atomic ensembles in the regime of electromagnetically induced transparency, that are capable of implementing all of the above prerequisites for deterministic optical quantum computation with single photons.
Quantum Computing on the Surface of Silicon
Zahra Shaterzadeh-Yazdi [IQIS, University of Calgary]
3 September 2008 - abstract -

Abstract:
Quantum computer executes quantum algorithms to solve computational problems. This feature enables such computer to excel over its classical
counterpart at some tasks, such as the exponential speedup in factorization of large prime integers. Here we present a novel architecture for quantum computer, which is quite promising based on today's nanotechnology achievements. In our scheme, information is encoded in charge qubits which are located on the Silicon surface. The charge qubit consists of an excess electron shared between a pair of dangling bonds. Logical single-qubit gates and transmission are performed by applying local electric fields. Coulomb interaction is considered to implement two-qubit gate. This scheme is proposed based on the recent successes of Dr. R. Wolkow and his group (NINT) on quantum cellular automata.
Adding and subtracting single photons to/from light fields and some other new results in manipulating the quantum states of light
Alessandro Zavatta [Istituto Nazionele di Ottica Applicara CNR c/o Physics Department, University of Florence]
8 August 2008 - abstract -

Abstract:
I will discuss some of the recent results obtained by the Quantum Optics Group of the Italian Institute for Applied Optics in Florence. In particular, I will discuss the experimental schemes to implement the action of single photon creation and annihilation operators on different kinds of basic quantum light states. The obtained states are then retrieved by means of quantum homodyne tomography which can reveal the density matrix, Wigner function and, in some particular cases, the Glauber P-function of the analyzed state. In addiction, I will show that when alternated sequences of the creation and annihilation operators are applied to a thermal state the resulting states depend on the order in which the two quantum operators are applied. In this way we can provide the most direct experimental verification of the non-commutation of bosonic operators.
One-way quantum computation in 4-d photonic states
Jaewoo Joo [IQIS, University of Calgary]
18 June 2008 - abstract -

Abstract:
We consider the possibility of performing linear optical quantum computation making use of extra photonic degrees of freedom. In particular we focus in the case where we use photons as quartit. The basic building block is a 2-quartit cluster state which is called a hyper-entangled state across polarization and two spatial mode
degrees of freedom. We examine the non-deterministic methods whereby such states can
be created from single photons and/or Bell pairs, and then give some mechanisms for performing higher-dimensional fusion gates.
A Few Open Problems in Quantum Information
Gilad Gour [University of Calgary]
2 May 2008 - abstract -

Abstract:
Quantum information science, an interface area of mathematics,physics and computing science, is concerned with the manipulation, computation and communication of information, where the information is encoded in two (or more) level quantum systems called "qubits", unlike classical
information, which is encoded in Boolean "bits". The devices used in this science are governed by the principles of quantum mechanics, which opens the possibility for a large range of applications. In this talk I will discuss several open problems in the field, focusing on the long standing additivity conjecture that the minimum entropy output of a completely positive trace preserving linear map, as measured using
the von Neumann entropy, is additive under taking tensor products. Despite the enormous effort by the most experts in the field during the last 12 years, this problem remained unsolved. Here I will present some recent
progress and future directions.

This talk is based on a joint work with N. R. Wallach and A. Roy.
The CHSH-Bell Inequality and Tsirelson's Bound with Postselection
Dominic Berry [Macquarie University]
30 April 2008 - abstract -

Abstract:
We find the necessary and sufficient condition on postselection for the CHSH-Bell inequality to hold for local realistic theories. This condition is weaker than the usual fair sampling assumption, demonstrating that the CHSH-Bell inequality will be valid under a wider variety of types of loss than previously believed. This condition implies that Tsirelson's bound must be satisfied for entangled states. On the other hand, if we restrict ourselves to a fixed set of measurements, it is possible for Tsirelson's bound to be violated while the CHSH-Bell inequality still holds for separable states. We present an experimentally feasible example for such violations.
On a semantics for higher order quantum computation
Benoit Valiron [Department of Mathematics and Statistics, University of Ottawa]
23 April 2008 - abstract -

Abstract:
I will briefly present what is higher-order computation and why it is worthwhile to consider it in the case of quantum computation. I will then sketch a language and describe some approaches to find a semantics for it. Finally I will explain what can be learned from this analysis.
Geometric squeezing of su(2) and su(1,1) observables
Hubert de Guise [Department of Physics, Lakehead University ]
16 April 2008 - abstract -

Abstract:
I will discuss squeezing properties of su(2) and su(1,1) intelligent states.

It will be seen how squeezing of appropriate observables can be automatically achieved if the correct intelligent state (of su(2) or su(1,1) ) can be prepared. This preparation can be done ��geometrically�� using group transformations and without recourse to a non-linear medium. A qualitative analysis, based on Wigner- and Q-functions will be presented to gain insight into the results.

Whether or not these states can be experimentally prepared is an open question.
Properties of Generic Subspaces
Jonathan Walgate [Perimeter Institute for Theoretical Physics ]
27 February 2008 - abstract -

Abstract:
We show how a simple fact of algebraic geometry translates into quantum information theory, determining when subspaces of multipartite Hilbert space have certain generic properties. In particular, we show when subspaces are completely entangled. This in turn implies other
results concerning the local distinguishability of random quantum states, the separability of random mixed states, the indistinguishability of random subspaces, and a mathematically interesting generalisation of Schmidt rank.
Quantum storage investigation in rare-earth ion doped crystals: The example of thulium
Thierry Chaneli�re [Laboratoire Aim� Cotton]
22 February 2008 - abstract -

Abstract:
Building a solid-state quantum memory for light is a very exciting and challenging task. More fundamentally it's also stimulating the creativity and giving us the opportunity to re-approach open problems within a different context. Thulium doped crystals have been widely studied but the disconcerting simplicity of the level structure seems to condemn it as a good candidate for quantum storage applications. I will show on contrary that this crystals can actually exhibit the features required by the storage protocols. The potentialities of Tm:YAG and Tm:Y2O3 will be discussed in this context. The particularly convenient wavelength is then a huge advantage over Pr and Eu based materials in which most of the experiment are currently performed. The first part of my talk will be dedicated to a long introduction of the domain of rare-earth ion doped crystals and their potentialities for quantum storage.
Plasmonics for Quantum Information Processing
Ali Kamli [Department of Physics , King Khalid University , Saudi Arabia]
23 January 2008 - abstract -

Abstract:
In the first part of this talk we review the idea of surface plasmon polaritons (SPPs) as surface waves at metal/nonmetal interface and calculate the dispersion curves and quantize the SPPs fields. In the second part of the talk we study the coupling of these modes to atomic systems. We show that SPPs can enhance or suppress the spontaneous decay rate of an atom near by and give numerical results. We also study the quantum entanglement of a two-qubit system interacting with a single mode SPP. We quantify entanglement in terms of negativity
measure and find an analytical expression for the time evolution of the negative eigenvalues for the partial transposition of the density operator in the presence of SPPs. The effect of the plasmonic excitation on entanglement dynamics is explored.
Bound entangled states and distillable key rate
Jeongsan Kim [IQIS, Department of Physics and Astronomy, University of Calgary]
16 January 2008 - abstract -

Abstract:
In this talk, we consider some sufficient conditions for quantum states to have positive distillable key rate [Phys. Rev. .A 75, 032306(2007)]. Exploiting the conditions, we show that the bound entangled states given by Horodecki et al. [Phys. Rev. Lett. 94, 160502 (2005), quant-ph/0506203] have nonzero distillable key rate, and finally exhibit new classes of bound entangled states with positive distillable key rate, but with negative Devetak-Winter lower bound of distillable key rate for the ccq states
of their privacy squeezed versions, which represent the states after the local measurement performed in the key part without considering the shield part. We will also consider the geometric distance and its lower bound of PPT bound entangled state from the set of private states for a fixed dimension.
On the Properties of nonMarkovian Master Equations
James Cresser [Department of Physics, Division of ICS, Macquarie University]
9 January 2008 - abstract -

Abstract:
All physical systems are to some extent open, and as a consequence the dynamics of such systems must be described in terms of a master equation. It is commonly the case that the master equation can be derived under the Born-Markov approximation, in which case the Markovian equation so derived assumes a particular form known as the Lindblad form. Lindblad master equations are much studied and an enormous amount is known about them. The situation is less clear in the non-Markovian case. In this talk, a review is given of some of the properties of non-Markov master equations, their derivation, interpretation and some properties of their solutions.

2007

DECOHERENCE: BASIC IDEAS
Philip Stamp [Pacific Institute for Theoretical Physics, Physics and Astronomy, University of British Columbia]
29 November 2007 - abstract -

Abstract:
I will review at an elementary level the ideas involved in decoherence. This will be done with liberal use of examples, taken from quantum optics, solid-state physics (superconductors, spin systems, nanoelectronics), and quantum computation. I will explain the 2 basic kinds of theoretical model (using spin and oscillator
baths) that are used to study decoherence in all these systems, emphasizing how these can be related to experiment, and also the open questions in the field. Since this is supposed to be a fairly general talk I will also discuss how questions about decoherence are related to larger issues in the foundations of quantum mechanics and non-equilibrium physics; and briefly describe some of the speculations surrounding the role of decoherence in
biology and cosmology.
Phase noise quenching in a four-level laser via squeezed vacuum
Javaid Anwar [Department of Physics, COMSATS Institute of Information Technology, Islamabad, Pakistan]
29 November 2007 - abstract -

Abstract:
It is shown by Gea-Banacloche "Phys. Rev Lett. 59, 543 (1987)" that the Laser Phase diffusion rate may be reduced by as much as one-half when laser is coupled out through a partially transmitting mirror to ��squeezed vacuum�� as opposed to ordinary vacuum. This happens for
a particular choice of the phase of the squeezed field. However, phase stability is not achieved for this choice of phase. In this paper, this analysis is extended by including a separate squeezed vacuum reservoir which couples the spontaneous decay between the lasing levels. The
results show that, it is possible to obtain the phase stability as well as phase noise quenching in this system.
DECOHERENCE at the MOLECULAR SCALE
Philip Stamp [Pacific Institute for Theoretical Physics, Physics and Astronomy, University of British Columbia]
28 November 2007 - abstract -

Abstract:
In what ways can decoherence be important for processes taking place at the molecular level? The answer to this question depends on the processes involved and on their timescale. We now know that the spin dynamics of both
large and small molecules is crucially affected by decoherence from the nuclear spin bath. It is interesting to ask how the charge dynamics of biological molecules, from DNA to proteins, might be affected by decoherence processes, and what the mechanism of these might be. It is also
important to ask to what use we might put insights gained in recent years from quantum
information theory and condensed matter physics, about how to control this decoherence. I will argue that quantum walk theory, supplemented by a
revised theory of error correction, will be very useful here. This talk will be a mixture of hard results and speculation.
Testing Quantum Devices: Entanglement Verification in Qubit-Mode Systems
Hauke Häseler [Institute for Quantum Computing, University of Waterloo]
28 November 2007 - abstract -

Abstract:
We present a method to test quantum behavior of quantum information processing devices, such as quantum memories, teleportation devices, channels and quantum key distribution protocols. The test of quantum behavior can be phrased as the verification of effective entanglement. Necessary separability criteria are formulated in terms of a matrix of expectation values in
conjunction with the partial transposition map. Our method is designed to reduce the resources for entanglement verification. A particular protocol based on coherent states and homodyne detection is used to illustrate the method. A possible test for the quantum nature of memories using two non-orthogonal signal states arises
naturally. Furthermore, closer inspection of the measurement process in terms of the Stokes operators reveals a security threat for
quantum key distribution involving phase reference beams.
Introducing quadratic form expansions
Niel deBeaudrap [Institute for Quantum Computing]
21 November 2007 - abstract -

Abstract:
I will present techniques to analyze unitary operations in terms of "quadratic form expansions", a form similar to a sum over paths where the phase of each path is described by a quadratic form over the reals. I will show how to relate such a form to an entangled resource akin to that of the one-way measurement model of quantum computing. Using this connection, we may consider various conditions under which it is possible to efficiently implement a unitary operation U, either when provided a quadratic form expansion for U as input, or by finding a quadratic form expansion for U from other input data.
Quantum computer simulations of time dependent Hamiltonians
Nathan Wiebe [Institute for Quantum Information Science, University of Calgary]
17 October 2007 - abstract -

Abstract:
When Feynman first introduced the idea of quantum computation, his motivation was to show that there is a way to efficiently simulate the complicated many body interactions that happen in quantum systems.
Since then a wide variety of schemes have been suggested to efficiently simulate time independent quantum systems on quantum computers, but as of yet no one has suggested a rigorous method that can simulate a time dependent quantum system on a quantum computer.

In this talk I will present a quantum algorithm that simulates an arbitrary finite dimensional time dependent Hamiltonian. This is important not only because it extends the range of Hamiltonians that are known to be simulateable on a quantum computer, but also because it allows us to rigorously compare the cost of emulating a Hamiltonian based model of quantum computation (such as adiabatic quantum computing) on a quantum computer.

I will also explicitly show that the resources required for the simulation scale near optimally with the simulation time, and that it scales efficiently with the system size if the Hamiltonian is sparse. I will also provide quantum circuits to clarify the operations needed to simulate a time dependent Hamiltonian. Finally applications of this simulation scheme to finding the cost of emulating Hamiltonian based quantum computing models (such as adiabatic
algorithms) on a circuit based quantum computer will also be discussed.
Mapping classical spin models to the graph state formalism
Maarten Van den Nest [Institut fur Quantenoptik und Quanteninformation, Osterreichische Akademie der Wissenschaften]
19 September 2007 - abstract -

Abstract:
We discuss how classical spin models, such as the Ising and Potts models on
arbitrary lattices, can be mapped to the stabilizer formalism. In
particular, we show how partition functions can be written as overlaps
between graph states and product states. These mappings allow to connect
concepts in (classical) statistical mechanics with quantum information
theory and to obtain a cross-fertilization between both fields. As a main
application, we prove that the 2D Ising model is "complete", in the sense
that its partition function contains the partition function of any other
spin model as a special instance. [joint work with W. Duer and H. Briegel]
Security in the Bounded Quantum Storage Model (iCIS seminar)
Juerg Wullschleger [McGill University]
12 September 2007 - abstract -

Abstract:
Due to a famous result by Mayers, and Lo and Chau, it is impossible to achieve bit commitment and
oblivious transfer in an unconditionally secure way, even in the quantum setting. Damgaard et al.
showed how to securely implement bit commitment and oblivious transfer in the bounded quantum storage
model, where the adversary is only allowed to store a limited number of qubits.

First, we review their protocols and security definitions and show that they are not strong enough
to imply composability. We will present a security framework for the bounded quantum storage model,
and show that our definitions imply that protocols can be composed sequentially. We show how the protocol
for oblivious transfer and the proof of its security need to be changed in order to achieve a secure
implementation in our model. Since our definitions are composable, a secure implementation of bit commitment
follows easily by a reduction to oblivious transfer.

This is joint work with Stephanie Wehner.
Authentication of Quantum Messages (iCIS seminar)
Juerg Wullschleger [McGill University]
11 September 2007 - abstract -

Abstract:
Quantum authentication allows a sender to send a quantum message (which may be unknown to him) \r\nto a receiver, in such a way that the receiver is able to check whether the message has been \r\nmodified during the transmission, either by noise or by an adversary.\r\n\r\nWe will present the solution to this problem by Barnum, Crepeau, Gottesman, Smith, and Tapp \r\nfrom 2002. We will first introduced some basics about quantum computation, including quantum \r\nteleportation and quantum error-correcting code, and then present a simple quantum authentication \r\nprotocol based on classical authentication and these basics primitives. Finally, in contrast \r\nto classical authentication, we show that any quantum authentication must also encrypt the message, \r\nand therefore the presented scheme is basically optimal.
Quantum hidden subgroup algorithms
Nolan Wallach [UC San Diego]
29 August 2007 - abstract -

Abstract:
Shor's algorithm for quantum factorization and discrete log
involves a reduction to his quantum algorithm for period search. This
can be interpreted as a hidden subgroup problem for a cyclic group.
In this lecture we will describe Shor's method and the extent that it
has been generalized in the literature (abelian groups, dihedral
groups, normal subgroups of non-abelian groups). We will then discuss
a new class of non-commutative groups for which there is a fast
quantum algorithm.
Local Hidden Variables Underpinning of Entanglement and Teleportation
Michael Revzen [Technion - Israel Institute of Technology]
8 August 2007 - abstract -

Abstract:
Entangled states whose Wigner representative functions are non-negative may
be viewed as being accounted for by local hidden variables (LHV = phase space
coordinates). We discuss studies of Bell's inequality violation with such states in
conjuction with Bell's theorem that precludes these violation for theories accountable
by LHV. We then consider if and underwhat conditions teleportation may be
accounted for with LHV. The study as whole is viewed as a study of entanglement.
Security proof against collective attack for the binary modulated continuous variable QKD.
YiBo Zhao [University of Science and Technology, China]
1 August 2007 - abstract -

Abstract:
We give the security proof against the collective attack for the
binary modulated reverse reconciliation continuous variable quantum key
distribution. The lower bound of the secret key rate is given based on
several observations. Bob's measurement is supposed to be homodyne detection
and his announcement is taken into account. The attack to the strong
reference pulse is not considered.
Exact quantum search algorithms of Grover's type
Zijian Diao [Ohio University Eastern Campus]
18 July 2007 - abstract -

Abstract:
Exact algorithms play an important role in both practical
applications and theoretical research. The original Grover's search
algorithm is probabilistic (not exact). Subsequent study provides several
exact quantum search algorithms which are guaranteed to succeed with
certainty. In this talk, we will first show that the original Grover's
algorithm is exact only when searching 1 out of 4. Then we will analyze
various designs of exact search algorithms with a few recent findings.
Information-theoretic security for authenticated long-distance quantum key distribution with partial trusted networks. (iCIS Security Seminar)
Barry Sanders [IQIS]
13 July 2007 - abstract -

Abstract:
Quantum key distribution must overcome two important hurdles: authentication to avoid the man-in-the-middle attack and relays or repeaters to allow long-distance communication. Current feasible approaches suggest complete trust of intermediate nodes in a network. We show that, in a network of partially trusted nodes (even with a low level of trust), our scheme enables probabilistic information-theoretic secure authentication and long-distance key distribution based on existing quantum key distribution technology, thus making our approach feasible now without reliance on total trust of intermediate nodes.
Su(2) and su(3) intelligent states
Benjamin Lavoie [Lakehead University]
25 April 2007 - abstract -

Abstract:
We show how all su(2) and su(3) intelligent states can be obtained by coupling su(2) and su(3) coherent states. The construction leads to a discussion of some general properties of these intelligent states.
Weighted complex projective 2-designs from bases
Aidan Roy [IQIS]
18 April 2007 - abstract -

Abstract:
We introduce the problem of constructing weighted complex projective
2-designs from the union of a family of orthonormal bases. If the weight remains
constant across elements of the same basis, then such designs can be
interpreted as generalizations of complete sets of mutually unbiased bases,
being equivalent whenever the design is composed of d+1 bases in dimension
d. We show that, for the purpose of quantum state determination, these designs
specify an optimal collection of orthogonal measurements. Using highly
nonlinear functions on abelian groups, we construct explicit examples from
d+2 orthonormal bases whenever d+1 is a prime power, covering dimensions
d=6, 10, and 12, for example, where no complete sets of mutually unbiased bases
have thus far been found. This is joint work with Andrew Scott.
A quantum study of slow light via electromagnetically induced transparency
Magnus Hsu [Australian National University]
11 April 2007 - abstract -

Abstract:
Using electromagnetically induced transparency (EIT), it is possible to delay and store light in atomic ensembles. Theoretical modelling and recent experiments have suggested that the EIT storage mechanism can be used as a memory for quantum information. We present experiments that quantify the noise performance of an EIT system for conjugate amplitude and phase quadratures. It is shown that our EIT system adds excess noise to the delayed light that has not hitherto been predicted by published conventional theoretical modelling. In analogy with other continuous-variable quantum information systems, the performance of our EIT system is characterised in terms of conditional variance and signal transfer.
Quantum Cryptography - Distinguished Lecture Series - CISaC & CMSS
Wolfgang Tittel [IQIS Calgary]
3 April 2007 - abstract -

Abstract:
The seventh and final talk in the Distinguished Lecture Series on Security, hosted jointly by the Centre for Information Security and Cryptography (CISaC) and the Centre for Military and Strategic Studies (CMSS).
Progress towards a quantum repeater
Matthew Eisaman [Harvard University & National Institute of Standards and Technology]
22 March 2007 - abstract -

Abstract:
I will discuss progress in our group towards the realization of a quantum repeater using atomic ensembles. First, I will review experiments performed in our lab over the last few years that demonstrated single-photon generation, and the slowing, storage, and retrieval of single-photon pulses using Electromagnetically Induced Transparency (EIT) in room-temperature atomic ensembles. I will then discuss future directions designed to improve these first proof-of-principle demonstrations to a level sufficient for real-world application.
Generation and Waveform Control of Narrow Bandwidth Paired Photons
Pavel Kolchin [Standford University]
1 March 2007 - abstract -

Abstract:
In the course of time spontaneous parametric down-conversion
in nonlinear crystals has become the near-standard method of generating
correlated and entangled photon pairs. The existing paired photon
sources based on crystals suffer from broad linewidth, short coherence
time and low spectral brightness. Recently a new approach to generation
of paired photons with long coherence time has been demonstrated by the
groups of M. Lukin and J. Kimble. They used EIT to generate single
photons on demand and to show non-classical correlations of paired
photons. More recently, S. Harris research group demonstrated generation
and rudimentary waveform shaping of narrow-band biphotons with high
spectral brightness. In this talk, I will give an overview of
experiments and theory done at Stanford on narrow-band paired photon
generation using cold Rb atoms. I analyze different regimes of
parametric down-conversion and discuss the influence of the optical
depth of the atomic sample and Langevin noise fluctuations on the
process. I also discuss the way to control the shape of generated paired
photons and outline the ways to improve the paired photon source.
The Power of Forgetting
Patrick Hayden [McGill University]
21 February 2007 - abstract -

Abstract:
Despite Landauer's early lesson that erasure plays a fundamental role in
understanding the physics of information, quantum information theorists
have been surprisingly slow to embrace erasure as a fundamental primitive.
Over the past year, however, it has become clear that a detailed
understanding of how difficult it is to erase correlations leads to a
nearly complete synthesis and simplification of the known results of
asymptotic quantum information theory. In fact, surprisingly many
all the tasks of interest, from distilling high-quality entanglement to
sending quantum data through a noisy medium to many receivers, can be
understood as variants of erasure. I'll sketch these developments before
making some speculations on applications to real physical systems.
On quantum algorithms for the graph isomorphism problem
Martin Roetteler [NEC Laboratories America]
16 February 2007 - abstract -

Abstract:
It is well-known that the graph isomorphism problem reduces
to a hidden subgroup problem (HSP) in the symmetric group. Moreover,
most exponential speedups in quantum computing are obtained by
solving HSP instances. Why is it then, that so far no polynomial quantum
algorithm for the graph isomorphism problem has been found?
We address this question by analyzing this HSP reduction and the
related quantum coset states. We show that entangled quantum
measurements on at least Omega(n log n) coset states are necessary to
get useful information, matching an information theoretic upper
bound.

Joint work with Sean Hallgren and Pranab Sen.
A simple nearest-neighbour two-body Hamiltonian system for which the ground state is a universal resource for quantum computation
Steve Bartlett [University of Sydney]
31 January 2007 - abstract -

Abstract:
We present a simple quantum many-body system - a two-dimensional lattice of
qubits with a Hamiltonian composed of nearest-neighbour two-body
interactions - such that the ground state is a universal resource for
quantum computation using single-qubit measurements. This ground state
approximates a cluster state that is encoded into a larger number of
physical qubits. The Hamiltonian we use is motivated by the projected
entangled pair states, which provide a transparent mechanism to produce such
approximate encoded cluster states on square or other lattice structures (as
well as a variety of other quantum states) as the ground state. We show that
the error in this approximation takes the form of independent errors on
bonds occurring with a fixed probability. The energy gap of such a system,
which in part determines its usefulness for quantum computation, is shown to
be independent of the size of the lattice. In addition, we show that the
scaling of this energy gap in terms of the coupling constants of the
Hamiltonian is directly determined by the lattice geometry. As a result, the
approximate encoded cluster state obtained on a hexagonal lattice (a
resource that is also universal for quantum computation) can be shown to
have a larger energy gap than one on a square lattice with an equivalent
Hamiltonian.
Dynamic Localization of Photons in Sinusoidally-Curved Waveguide Arrays
Mirko Lobino [Politecnico di Milano]
26 January 2007 - abstract -

Abstract:
The electron motion in a crystalline potential subjected to an
external sinusoidal electric field reveals an interesting coherent
dynamical phenomenon called dynamic localization (DL). This phenomenon
consists of a periodic relocalization of the electronic wave function
under the action of an external field with proper amplitude and frequency,
as it was theoretically predicted by Dunlap and Kenkre in 1986. Curved
waveguide arrays provide an ideal laboratory system for visualizing DL
since the paraxial wave equation for the electromagnetic field is formally
identical to the Schr�dinger equation for the electron wavefunction in a
periodic potential under the action of an external field.
Universal quantum computation in decoherence-free subspace with neutral atoms
Peng Xue [IQIS]
24 January 2007 - abstract -

Abstract:
We show how realistic cavity-assisted interaction between neutral
atoms and coherent optical pulses, and measurement techniques, combined
with optical transportation of atoms, allow for a universal set of quantum
gates acting on decoherence-free subspace (DFS) in deterministic way. The
logical qubits are immunized to the dominant source of
decoherece----dephasing; while, the influences of additional errors are
shown by numerical simulations. We analyze the performance and stability of
all required operations and emphasize that all techniques are feasible with
current experimental technology.
On the Role of Shared Entanglement
Dmitry Gavinsky [IQC, University of Waterloo]
10 January 2007 - abstract -

Abstract:
Despite the apparent similarity between shared randomness and
shared entanglement in the context of Communication Complexity, our
understanding of the latter is not as good as of the former.
In particular, there is no known " entanglement analogue" for the
famous theorem by Newman, saying that the number of shared random
bits required for solving any communication problem can be at most
logarithmic in the input length (i.e., using more than O(log(n))
shared random bits would not reduce the complexity of an optimal
solution).

We prove that the same is not true for entanglement.
We establish a wide range of tight (up to logarithmic factors)
entanglement vs. communication trade-offs for relational problems.
We show that relatively small increase in the number of available
qubits of entanglement can lead to much more efficient solution, the
gain is exponential in some cases.

2006

Concealing Entanglement in Classical Bits
Gilad Gour [MITACS discrete math seminar, University of Calgary]
8 December 2006 - abstract -

Abstract:
Entanglement and in particular bipartite entanglement is the key resource for many quantum information processing tasks. Thus, it is extremely important to find secure ways to distribute entanglement among distant parties. In this talk I will discuss several methods to conceal entanglement in classical bits and focus on the hidden entanglement, the entanglement of assistance, the localizable entanglement and the entanglement of collaboration. In particular, I will show that one classical bit can unlock at most one ebit.
An all-fibre diet for quantum information processing
Felix Bussieres [Ecole Polytechnique de Montreal]
23 November 2006 - abstract -

Abstract:
The equivalent of almost every bulk optical component can be fabricated
with fibre optics only. I will review some of the work we have done in
designing and fabricating these components and discuss the benefits of
all-fibre technology for quantum information processing. In particular,
I will describe our recent experiments for creating efficient and
untrusted quantum key distribution networks.
A Fast Deterministic Algorithm for Solving Quantum Games
Gus Gutoski [University of Waterloo]
15 November 2006 - abstract -

Abstract:
A game can be modelled as an exchange of messages between two competing
players and a referee, after which the referee chooses a winner. In a
quantum game the players and referee may perform quantum computations and
exchange quantum messages. In this talk we examine the problem of deciding,
given a fixed quantum referee, which of the two players has a winning
quantum strategy. We give a deterministic algorithm that decides quantum
games in time exponential in the number of qubits exchanged throughout the
game between the referee and players.

Our algorithm subsumes previously known algorithms for solving classical
games. Moreover, it implies that the quantum games model of computation is
no more powerful than its classical counterpart. In terms of complexity
classes, we have QRG = RG = EXP, offering a rare quantum characterization of
a classical complexity class.
Strengthening the adversary method with negative weights
Troy Lee [LRI, Universite Paris-Sud]
1 November 2006 - abstract -

Abstract:
The quantum adversary method, along with the polynomial method, is one
of the most successful techniques for proving lower bounds on quantum
query complexity. The adversary method, originally developed by
Ambainis, has recently received a lot of attention with several
authors giving generalizations and alternative formulations. These
include formulations in terms of weight schemes [Amb03,Zha05],
eigenvalues of matrices [BSS03], and Kolmogorov complexity
[LM04]. Using the duality theory of semidefinite programming, Spalek
and Szegedy show that all of these formulations of the adversary
method are in fact equivalent.

We present a strengthening of the adversary method. This new method
gives a lower bound on bounded-error quantum query complexity, is
always at least as large as the adversary bound, and can sometimes be
much larger: we show that for every m, there is a function f whose
adversary bound is less than m and where the new bound is larger than
m^{1.09}. We also show that this new bound does not face the
``certificate complexity'' barrier which limits the old adversary
method. The new bound is obtained by allowing matrices with negative
entries in the matrix formulation of the adversary method.

Joint work with Peter Hoyer and Robert Spalek.
Bit concealment in GHZ states
Anirban Roy [ICTP, Trieste]
25 October 2006 - abstract -

Abstract:
In an usual (k,n) threshold quantum secret sharing sceme, a secret
quantum state is divided among n parties, such that any k of them can
reconstruct the state, while any set of k-1 or fewer parties cannot. Here we
propose a bit concealment idea in a set of GHZ states where unless all
parties collaborate, they cannot learn the bit even with LOCC.
Block Ciphers: From Shannon to Rijndael
Kjell Wooding [University of Calgary]
19 October 2006 - abstract -

Abstract:
Even today, in the age of public-key and quantum cryptography, block
ciphers and symmetric cryptography still form the heart of most
practical cryptosystems. This talk will trace the development of the
block cipher, from Claude Shannon's original conception of the product
cipher, through their popularization in the form of Feistel networks
and the Data Encryption Standard, and finally on to their most modern
incarnation -- the Advanced Encryption Standard.
Quantum Control Optimization in Circuit Mode
Dmitri Maslov [Institute for Quantum Computing, University of Waterloo]
11 October 2006 - abstract -

Abstract:
Most quantum circuits are time-dependent diagrams
describing the process of quantum computation. And, most often,
quantum algorithms must be mapped into a quantum circuit to be able
to run them on quantum hardware. Optimal synthesis of quantum
circuits is intractable and heuristic methods must be employed,
resulting in non-optimal circuit specifications. In this talk, I will
consider the problem of optimizing quantum circuits for better
performance. In particular, two methods, one designed for reducing
the weighted gate count and the other designed for optimizing the
time delay will be introduced. The methods will be discussed
generically, making it clear how they can be applied to the
simplification of quantum circuits constructed with different types
of quantum gates and in different technologies. For the purpose of
experimental testing, a gate library composed of NOT, CNOT, and
controlled-sqrt-of-NOT gates is chosen. Proposed underlying
technology is assumed to be liquid NMR. I will illustrate in detail
how the methods apply to simplify some small quantum circuits, such
as adders and small oracles. I will also present and discuss the
results of simplification of larger designs, e.g. multiple control
Toffoli gate (with positive and/or negative controls) implementations
and some arithmetic circuits (adders, comparators, and modular
exponentiation circuits) that were recently reported in the
literature.
Quantum Electrodynamics Based on Self-Fields
Jonathan Dowling [Hearne Institute for Theoretical Physics, Louisiana State University in Baton Rouge]
6 October 2006 - abstract -

Abstract:
In an extension of the neoclassical theory of Jaynes, which itself an
independent rediscovery of an old idea by Fermi, we will discuss the
Self-Field Electrodynamics of Barut and show how this semiclassical
theory can be used to recover such QED effects as spontaneous
emission, Lamb shift, and g-2, all without field second quantization.
We will also discuss how the Jaynes neoclassical theory was limited
by the two-level approximation, which is removed in the Barut theory.
The self-field theory agrees with full QED in all cases computed so
far, up to first order in the fine structure expansion.
A Rubidium Atom Magneto-Optic Trap for Experimental Characterization of EIT
Shannon Mayer [University of Portland]
5 October 2006 - abstract -

Abstract:
Laser cooling and magneto-optic trapping of neutral atoms is a relatively
simple but effective tool for producing high-density (10^10 atoms/cm^3),
low-temperature (< 20 microK) atomic samples. Trapped samples have been
used for experiments in optical spectroscopy, microwave spectroscopy,
and cold-atom collisions, and as a starting point for atom interferometry
and Bose-Einstein condensation. In this talk I will briefly discuss the
theory behind cooling and trapping of neutral atoms and describe the
experimental apparatus for a magneto-optic trap constructed by
undergraduate physics students at the University of Portland. Avenues
for investigation and characterization of electromagnetically-induced
transparency in laser cooled atomic rubidium will also be discussed.
Spectroscopic appplication of biphoton's interference.
Dmitry Korystov [University of California, Santa Barbara]
21 September 2006 - abstract -

Abstract:
Two sources of biphoton fields divided by a gap filled with an arbitrary
media allow to measure dispersive properties of the media inside gap in a
wide spectral region. The origin of the method is a modification of the
angle-frequency line shape of spontaneous parametric scattering due to
interference of biphoton fields modified by absorption and dispersion in
gap. This scheme can be described as a non-linear Mach-Zender interferometer.
Donor and superconducting quantum computer architectures: challenges and prospects
Austin Fowler [IQC, University of Waterloo]
20 September 2006 - abstract -

Abstract:
After a review of the physical resources required to efficiently implement quantum error correction and fault-tolerant computation, I describe the latest ideas of how one might build a quantum computer using firstly phosphorus atoms in silicon and secondly superconducting components. In both cases, fundamentally unscalable ideas such as field gradients, fixed frequency selectivity, and serial gates are avoided. Global oscillating fields and high qubit densities leading to severe crosstalk problems are also avoided. Indeed, the architectures presented can be scaled to arbitrarily large numbers of qubits without making the construction or operation of a fixed unit length of the computer any more difficult.
Measuring h/MCs using atom interferometry
Chris Vo [Physics Department, Stanford University]
11 September 2006 - abstract -

Abstract:
We present an atom interferometry experiment to determine the photon recoil shift of the cesium D2-line and thereby the ratio h/M. Here, h is Planck's constant and M the mass of a cesium atom. Knowing h/M to high accuracy is crucial for a determination of the fine structure constant a without involving higher order Quantum Electrodynamical (QED) calculations. Our accuracy goal is 10^-9 for the relative uncertainty h/M. This will allow the most precise test of QED and the Standard Model by comparing the resulting value for a with a recent determination based on a measurement of the electron's anomalous magnetic moment. Our setup will use simultaneous conjugate Ramsey-Borde atom interferometers in an atomic fountain. The beam splitters will be implemented by multiphoton Bragg diffractions in standing wave light fields.The talk will focus on the interferometric technique in use and the choice of atom optics. Discussed technical aspects will include a highly phase-stable laser system for the beam splitter pulses and an automatic alignment system for the counterpropagating interferometer beams.
Adiabatic passage through space: Robust coherent transport in solid-state systems
Andy Greentree [Centre for Quantum Computer Technology, School of Physics, The University of Melbourne]
24 August 2006 - abstract -

Abstract:
Stimulated Raman Passage (STIRAP) is a technique for transferring
population between atomic energy levels in a three-state system. Hallmarks
of this technique are its robustness, the surprising mechanism for
population transfer where the enabling pulses are applied in the
counter-intuitive direction, and that population is never found in the
intermediate state. Exploiting quantum coherence in solid-state systems
allows us to consider performing a STIRAP like protocol on a spatially
defined triple-dot arrangment. We call this CTAP (Coherent Tunneling
Adiabatic Passage). Like STIRAP, this protocol is robust, and population
is transferred from the left to the right dot, without ever populating the
central dot (even transiently). This procedure can be extended to
consider transport through long chains, and to multiple recipients for
distributed entanglement generation, and operator measurement QC. We have
also formulated a new quasi-2D architecture incorporating based on CTAP.
The Theory of Quantum Electromechanics
Elinor Irish [University of Rochester]
21 August 2006 - abstract -

Abstract:
"Quantum electromechanics" combines a superconducting qubit and a
nanofabricated mechanical resonator into a system similar to an atom in an
optical cavity. Many fascinating quantum optical effects should be
realizable in this solid-state system. Additionally, new effects may
appear due to the possibility of very strong coupling even at large
detunings. I will talk about my work on the theory of quantum
electromechanical systems, motivated in particular by the search for ways
to observe the quantum behavior of nanoscale mechanical resonators.
Experimental Manipulation of Multi-photon Entanglement towards Quantum Information Processing
Anning Zhang [Department of Physics, University of Toronto]
11 August 2006 - abstract -

Abstract:
Multi-photon entanglement plays an important role in both the fundamental tests of quantum mechanics vs. local realism and quantum information processing. In my talk, I will present several results about experimental manipulation of three- four- and five-photon nentanglement.
A fault-tolerant one-way quantum computer
Robert Raussendorf [Perimeter Institute for Theoretical Physics]
28 July 2006 - abstract -

Abstract:
Describe a fault-tolerant one-way quantum computer on cluster states in three dimensions. The presented scheme uses methods of topological error correction resulting from a link between cluster states and Kitaev's surface codes. A quantum circuit is realized by choosing appropriate boundary conditions for the 3D cluster. The error threshold is 0.11 percent for each source in an error model with preparation-, gate-, storage- and measurement errors.
Decohering quantum walks: exploring the space between quantum and classical computing
Viv Kendon [Physics and Astronomy, University of Leeds]
26 July 2006 - abstract -

Abstract:
Quantum versions of random walks have markedly different properties from
classical random walks, such as faster spreading and mixing. These
properties have been exploited to create several quantum algorithms. It has
also been observed that making the quantum walk slightly less than perfectly
quantum can actually improve the useful behaviour, such as even faster
mixing to the uniform distribution. We have calculated the entanglement
between the coin and position, and find that the optimal computational
behaviour occurs just at the point all the entanglement has been removed by
the decoherence. Combined with recent work by others, this provides several
interesting perspectives on the phenomenon and its usefulness.
Efficient generation of VUV radiation in coherently prepared mercury vapour
Martin Oberst [ Fachbereich Physik Technische Universitaet Kaiserslautern]
24 May 2006 - abstract -

Abstract:
The enhancement of the generation of tunable vacuum ultra violet radiation at 125nm in atomic Hg vapor prepared in a state of maximum coherence is presented. The enhancement is accomplished by using a two-photon Stark chirped rapid adiabatic passage (SCRAP)-technique. This technique uses strong, off-resonant, pulsed electromagnetic fields in the infrared spectral region (1064nm) which generate dynamic Stark shifts in the nonlinear medium. These stark shifts are used to continuously tune the transition frequency of a two photon resonance in Hg which is addressed
by a near resonant pump field at 313nm. Under certain conditions this leads to an adiabatic transfer process from the ground state to the 7s $^1S_0$ state of Hg which results in an complete population transfer to this state. As a consequence a maximum, transient coherence is prepared between the corresponding levels. This maximum coherence can be used to enhance the efficiency of the nonlinear four wave mixing process which generates the VUV radiation. The achieved enhancement is more than one order of magnitude with respect to conventional frequency conversion.
Parallelizing Quantum Circuits
Anne Broadbent [Universit� de Montr�al]
17 May 2006 - abstract -

Abstract:
Given a quantum circuit, an interesting question both from the theoretical
and practical viewpoints the following: "Can this circuit be
parallelized?" In this talk, I show how tools developed in the
measurement-based model for quantum computation can be used to parallelize
certain families of quantum circuits, thus partially answering the above
question. This talk is based on joint work with Elham Kashefi.
Implementation of multipartite unitary operations with limited resources
Dominic Berry [University of Queensland]
12 May 2006 - abstract -

Abstract:
In quantum information processing it is often necessary to perform
operations between qubits (or qudits) which do not directly interact. It
is therefore important to know what resources are needed to achieve these
operations. In particular, if the interaction is weak it would be
desirable to implement it using only a small amount of entanglement and
communication.
I show that it is possible to implement evolution under multipartite
tensor product Hamiltonians using a small amount of entanglement and a
small amount of communication in some of the directions. This improves on
previous work in three main ways:
1. Previous work only considered simple cases, such as bipartite two-qubit
unitaries. This method applies for general multipartite tensor product
Hamiltonians. It may also be applied to sums of these Hamiltonians via the
Trotter formula.
2. The entanglement required is only 5.6418t|H|. In contrast, the
entanglement required for the scheme of Cirac, D�r, Kraus and Lewenstein
(which is limited to the two-qubit Ising interaction) requires
entanglement of 5.9793t|H|.
3. For many implementations, compression is used to achieve the
implementations using average communication in some of the directions as
low as the entanglement. The scheme of Cirac, D�r, Kraus and Lewenstein
requires a large amount of communication.
Equiangular lines, mutually unbiased bases, and difference sets
Aidan Roy [University of Waterloo]
11 May 2006 - abstract -

Abstract:
In 1975, Delsarte, Goethals and Seidel found an upper bound
for the size of a "system of complex lines": a set of vectors whose
scalar products have only a small number of distinct absolute values.
Recently, applications in quantum tomography have renewed interest in
constructing systems of maximal size. We consider two particular
problems: equiangular lines, which are sets in which only one
absolute value occurs; and mutually unbiased bases, in which two
values occur and the lines are partitioned into orthonormal bases.
For real vector spaces, these systems are closely related to regular
two-graphs and Hadamard matrices. However, the complex versions are
not nearly as well understood.

In this talk, we will see that combinatorial structures such as
difference sets and Cayley graphs can also be used for constructions
in complex case. In particular, we use difference sets in abelian
groups to produce equiangular lines, and we use relative difference
sets to produce maximal sets of mutually unbiased bases.

This talk is based on joint work with Chris Godsil.
Introduction to relativistic quantum information
Daniel Terno [Perimeter Institute for Theoretical Physics]
10 May 2006 - abstract -

Abstract:
I discuss the role that relativistic considerations play in quantum
information processing. First I mention how the causality requirements
limit possible multi-partite measurements. Then the Lorentz
transformations of quantum states are introduced, and their implications
on physical qubits are described. This is used to describe relativistic
effects in communication and entanglement.
Many particle quantum walks
David Feder [IQIS]
29 March 2006 - abstract -

Abstract:
The quantum walk (QW) is the quantum mechanical extension of the
classical random walk, where the quantum particle (the walker) can be
considered to follow many trajectories simultaneously. The quantum
walker can often traverse graphs more quickly than using any classical
scheme, an advantage that can be harnessed for fast quantum algorithms.
Motivated by recent experiments on ultracold atoms in optical lattices,
I will explore the properties of many particle quantum walks. I will
discuss two main results. First, these walks can provide in situ
experimental signatures of both the Mott-insulator phase transition and
fermionization. Second, a duality between many-particle and
single-particle quantum walks reveals that a quantum walker can fully
traverse certain one and two-dimensional weighted graphs in constant
time, even when the number of vertices grows exponentially, hitting the
output vertex with 100\% probability.
General Setting for Geometric Phase of Mixed States in Open Systems
Ali Rezakhani [IQIS]
8 March 2006 - abstract -

Abstract:
In this talk, the problem of a geometric phase for an open quantum system
is described in a unifying approach. Two of the existing methods to
define geometric phase, one by Uhlmann's approach and the other by a
kinematic approach, which have been considered to be distinct, are shown
to be related in this framework. The method is based on purification of
a density matrix by its uniform decomposition, and hence, a generalization
of the parallel transport condition. It is also shown how to recover the
earlier known definitions of geometric phase as well as how to generalize
them when degeneracy exists and varies in time.
Photon generation for quantum information
Nick Peters [University of Illinois]
12 January 2006 - abstract -

Abstract:
According to Schroedinger, ``Entanglement is the characteristic trait of quantum mechanics.'' But for an idea that has been around since the first half of the twentieth century, the most simple entangled quantum system a pair of two-level systems still yields new and interesting physics. We will discuss generation of exotic entangled photon pairs, their ``concentration,'' and how their quantum nature enables a non-intuitive form of quantum communication called remote state preparation. Further, we will examine several ways of benchmarking entangled states. Finally, we will discuss progress on a quasi-deterministic single-photon source based on spontaneous parametric downconversion.

2005

Quantum Phase Transitions and Entanglement
Junru Wu [University of Vermont]
12 December 2005 - abstract -

Abstract:
We develop a general theory of the relation between quantum phase transitions (QPTs) characterized by nonanalyticities in the energy and entanglement measures. We notice a functional relation between the matrix elements of two-particle reduced density matrices and the eigenvalues of general two-body Hamiltonians of $d$-level systems. The ground state energy eigenvalue and its derivatives, whose non-analyticity characterizes a QPT, are directly tied to bipartite entanglement measures. We show that first-order QPTs are signalled by density matrix elements themselves and second-order QPTs by the first derivative of density matrix elements. Our general conclusions are illustrated via several quantum spin models.
Distributed quantum information processing
Ujjwal Sen [IFCO, Barcelona]
1 December 2005 - abstract -

Abstract:
Quantum information is an emerging science, the results of which, influence many disciplines, ranging through atomic and molecular physics, quantum optics, condensed matter physics, to technology. It predicts spectacular applications like efficient factorization of prime numbers and secure cryptography. For an efficient performance of such tasks, it is important to understand the flow of information distributed over macroscopic or mesoscopic systems, as well as that between separated systems. I will present current research on the quantum mechanical bounds on capacities of communication channels, dynamics of quantum correlations in spin systems, and possibility of fault tolerant quantum computation in quantum neural networks.
Bell experiments: Traps and pitfalls
Andr� Allan M�thot [Universit� de Montr�al]
29 November 2005 - abstract -

Abstract:
In this talk, I present different misconceptions concerning elements of realism, locality, contextuality, Bell experiments, pseudo-telepathy, etc. Unfortunatly, these appear too often in the literature and I will use some examples from recent articles by Greenberger, Horne and Zeilinger, and by Cabello [quant-ph/0511047].
More on the Adiabatic Approximation in Quantum Mechanics
Richard MacKenzie [Universit� de Montr�al]
29 November 2005 - abstract -

Abstract:
A new and intuitive perturbative approach to time-dependent quantum mechanics problems is presented, which is useful in situations where the evolution of the Hamiltonian is slow. The state of a system which starts in an instantaneous eigenstate of the initial Hamiltonian is written as a power series which has a straightforward diagrammatic representation. Each term of the series corresponds to a sequence of "adiabatic" evolutions, during which the system remains in an instantaneous eigenstate of the Hamiltonian, punctuated by transitions from one state to another. The first term of this series is the standard adiabatic evolution, the next is the well-known first correction to it, and subsequent terms can be written down essentially by inspection. Although the final result is perhaps not terribly surprising, it seems to be not widely known, and the interpretation is new, as far as we know. Application of the method to the adiabatic approximation is given, and some discussion of the validity of this approximation is presented.
Zero-knowledge against quantum attacks
John Watrous [Institute for Quantum Information Science, University of Calgary]
23 November 2005 - abstract -

Abstract:
It has been a difficult problem in theoretical quantum cryptography for several years to formulate a general and cryptographically meaningful definition of quantum zero-knowledge and to apply the definition to non-trivial protocols. In this talk I will explain how this problem can be solved, at least to a significant extent, for what are arguably the strongest and most natural definitions of quantum zero-knowledge.
Symmetry breaking and contraction via Kac-Moody formalism
Jamil Daboul [Ben Gurion University of the Negev, Israel]
22 November 2005
Informationally complete quantum measurements
Andrew Scott [Institute for Quantum Information Science, University of Calgary]
21 November 2005 - abstract -

Abstract:
An informationally-complete quantum measurement (IC-POVM) is a measurement described by a positive operator-valued measure (POVM) which has the property that every quantum state is uniquely determined by its measurement statistics. Consequently, given multiple copies of an unknown state, a sequence of measurements will give an estimate of the statistics, and hence, identify the state itself. This process is called quantum state tomography.

In the context of quantum information theory, two important examples of IC-POVMs have been studied: complete sets of mutually unbiased bases (MUBs) and symmetric informationally-complete POVMs (SIC-POVMs). The former is prescribed by a set of orthogonal von Neumann measurements while the latter is a POVM consisting of subnormalized pure-state projectors. Both are statistically unbiased and both have the minimum number of elements possible for an IC-POVM of their type: d+1 bases and d2 POVM elements, respectively, where d is the dimension of the quantum system under study.

In this talk I will present an introduction to informationally-complete quantum measurements and then a detailed study of the two above-mentioned types. We will make use of frame theory to give IC-POVMs a mathematical structure and relate the two above-mentioned types to complex projective designs. Open problems and other types of IC-POVMs will also be considered.
Economical and noisy one-way quantum computing.
Mark Tame [Queen's University, Belfast, UK]
16 November 2005 - abstract -

Abstract:
First, I would like to introduce several aspects of cluster-state quantum computing in the presence of noise and decoherence [1]. This will then allow me to talk in more detail about recent developments in economical strategies for quantum information processing [2, 3], that greatly improve the efficiency and scalability of the original "one-way model for quantum computation" [4, 5]. Then, I will go on to discuss some details concerning compact cluster configurations for two very interesting quantum algorithms [6, 7]. One of these [6] has recently been experimentally performed in Vienna and the other [7] is certainly feasible with current all-optical technology.

References:
[1] M. S. Tame et al. quant-ph/0412156 (2004); M. S. Tame et al. Phys. Rev. A 72, 012319 (2005).
[2] M. S. Tame et al., quant-ph/0507173 (2005).
[3] S. C. Benjamin et al., New J. Phys. 7, 194 (2005).
[4] R. Raussendorf & H. J. Briegel, Phys. Rev. Lett., 86, 5188-5191 (2001).
[5] R. Raussendorf, D. E. Browne & H. J. Briegel, Phys. Rev. A 68, 022312 (2003).
[6] P. Walther et al., Nature 434 169 (2005).
[7] M. Paternostro et al. quant-ph/0509066 (2005) [to appear in NJP].
Simulating quantum correlations as a sampling problem. Joint work with Julien Degorre and Jeremie Roland (LRI).
Sophie Laplante [LRI]
9 November 2005 - abstract -

Abstract:
It is known that quantum correlations exhibited by a maximally entangled qubit pair can be simulated with the help of shared randomness, supplemented with additional resources, such as communication, post-selection or non-local boxes. For instance, in the case of projective measurements, it is possible to solve this problem with protocols using one bit of communication or making one use of a non-local box. We show that this problem reduces to a distributed sampling problem. We give a new method to obtain samples from a biased distribution, starting with shared random variables following a uniform distribution, and use it to build distributed sampling protocols. This approach allows us to derive, in a simpler and unified way, many existing protocols for projective measurements, and extend them to positive operator value measurements. Moreover, this approach naturally leads to a local hidden variable model for Werner states.

quant-ph/0507120
Classical and Quantum Function Reconstruction in Finite Fields.
Igor Shparlinski [Macquarie University, Sydney, Australia]
4 November 2005 - abstract -

Abstract:
Motivated by applications to pseudorandom generators and stream ciphers, we consider the problem of reconstruction of a function $f: F_p -> R$ defined on elements of a finite field and with real values. Examples includes: $f(x) = (x+s/p)$, the Legendre symbol, or $f(x) = MSB_k(g(x))$, $k$ most significant bits of the reduction of $g(x)$, where $g: F_p -> F_p$. In this problems the shift $s$, the functions $g$ (and sometimes the prime $p$) are unknown. We will give a short survey of known classical and quantum algorithms and try to exhibit some main ideas behind the proofs. mainly of number theoretic nature. We will also outline some open questions and directions for further research.
In defense of the epistemic view of quantum states: a toy theory
Rob Spekkens [Perimeter Institute, Waterloo]
2 November 2005 - abstract -

Abstract:
What would it be like to live in a world where observers were faced with a fundamental restriction on how much knowledge they could acquire about the states of systems around them? I attempt to answer this question in a particularly simple context, where an observer's knowledge is characterized by a number of yes/no questions, and where the restriction on knowledge has a particularly simple form: the number of questions that are answered is always less than or equal to the number of questions that are unanswered. Remarkably, given a few other assumptions about this toy universe, one obtains a richly structured theory that qualitatively reproduces a wide variety of quantum phenomena. Such phenomena include the non-commutativity of measurements, the impossibility of discriminating non-orthogonal states, interference, various features of entanglement, the no cloning theorem, quantum teleportation, and many others. The quality and diversity of these analogies provides compelling evidence for the view that quantum states are states of incomplete knowledge rather than states of reality. A consideration of the phenomena that the toy theory fails to reproduce, notably, violations of Bell inequalities and the existence of a Kochen-Specker theorem, provides clues for how to proceed with this research program.
Is entanglement sufficient to quantify quantum non-locality?
Gilad Gour [University California, San Diego, USA]
1 November 2005 - abstract -

Abstract:
I will show that a finite number of conditions are {\em not} sufficient to determine the locality of transformations between two $d\times d$ mixed states with $d\geq 4$, as well as the locality of transformations between two probability distributions of pure states. A natural question is then arise: is an infinite number of conditions sufficient? In other words, is entanglement sufficient to quantify non-locality in quantum mechanics? As a simple example, I will present an infinite, but minimal, set of necessary and sufficient conditions for the existence of a local procedure that converts one probability distribution of two pure pair of qubits into another.
Measurement-based Quantum Computation
Simon Perdrix [IMAG, Grenoble, France]
19 October 2005 - abstract -

Abstract:
Are the Minimal Resources Reached ? Projective measurements are universal for quantum computation, i.e. any unitary transformation can be simulated by means of projective measurements only. The original proof by Nielsen [1] is based on generalized teleportation. This model has been successively improved [2,3], reducing the resources (i.e. the size of the measurements and the number of ancillary qubits) used to simulate any unitary transformation. I will present the last improvement, based on state transfer [3], and analyze which resources are required to simulate any unitary transformation, trying to answer the question: Are the minimal resources reached?

[1] M. A. Nielsen. Universal quantum computation using only projective measurement, quantum memory, and preparation of the 0 state, Phys. Lett. A. 308 (2-3): 96-100 (2003).

[2] D. W. Leung. Quantum computation by measurements, International Journal of Quantum Information, Vol. 2, No. 1 (2004) 33-43.

[3] S. Perdrix. State Transfer instead of Teleportation in Measurement-based Quantum Computation, International Journal of Quantum Information, Vol. 3, No. 1 (2005) 219-223.
Quantum Information Processing with 1010 electrons?- A short review of surface plasmon physics, recent experiments and proposals
Ren� Stock [Institute for Quantum Information Science, University of Calgary]
12 October 2005 - abstract -

Abstract:
Surface plasmon polaritons are optically excited, macroscopic charge-density oscillations involving 1010 electrons at the surface of conducting matter. Recent entanglement preserving experiments have shown evidence of the quantumness of surface plasmons, despite the macroscopic nature of these surface excitations. The goal of this presentation is to give a short overview over the 50-year-old field of surface plasmon physics and to evaluate the usefulness of surface plasmons for quantum information processing implementations.
Topological Quantum Computing with Anyons
Alexis Morris [Institute for Quantum Information Science, University of Calgary]
5 October 2005 - abstract -

Abstract:
Since the advent of error correction codes, it is theoretically possible to perform quantum computations to any desired accuracy, provided that the failure rate for the quantum gates is smaller than a certain threshold value. However, it will still be some time (if ever!) before experimental techniques can be perfected in order to get below this threshold error rate. This is where topological quantum computation comes into play. The idea is to use a Hilbert space that is instrinsically robust against decoherence effects to perform the quantum computations. In this talk I will introduce the ideas behind topological quantum computation (TQC), starting with the concept of anyons. I will show how anyons can be used to perform TQC and conclude by showing how topological quantum gates can be implemented by braiding anyonic quasi-particles.
Magic States.
Nathan Babcock [Institute for Quantum Information Science, University of Calgary]
28 September 2005 - abstract -

Abstract:
The Gottesman-Knill theorem states that quantum computations consisting only of preparations of the |0> state, unitary operations from the Clifford group, and Pauli measurements can be simulated efficiently on a classical computer and are therefore not sufficient to do universal quantum computation (UQC). Recently, Bravyi and Kitaev proposed a novel scheme for UQC based on a modification to the Clifford group model (quant-ph/0403025). They show that known quantum error correction algorithms will distill certain "magic" mixed states into pure states allowing UQC. I will provide a brief review of quantum error correction and the "stabilizer" formalism before giving a detailed explanation of the distillation algorithm. Finally, I will discuss a "proof-of-concept" implementation of the algorithm on a nuclear magnetic resonance quantum computer.
Degradation of a directional quantum reference frame.
Peter Turner [Institute for Quantum Information Science, University of Calgary]
21 September 2005 - abstract -

Abstract:
I will go through the details of the degradation of a directional quantum reference frame with repeated measurements of spin one-half systems. Although a closed form solution for the state of the frame after N spins have been measured eludes me, I do have a solution for the average error rate.
Factorizations and Representations in a Finite Space
Ady Mann [Technion, Israel]
14 September 2005 - abstract -

Abstract:
A Hilbert space in M dimensions is shown explicitly to accommodate representations that reflect the prime numbers decomposition of M. Representations that exhibit the factorization of M into two relatively prime numbers (the kq representation and related representations termed $q_{1}q_{2}$ representations (together with their conjugates)) are analysed, as well as a representation that exhibits the complete factorization of M. In this latter representation each quantum number varies in a subspace that is associated with one of the prime numbers that make up M.
Quantum and Classical Strong Direct Product Theorems and Optimal Time-Space Tradeoffs
Robert �palek [CWI]
23 August 2005 - abstract -

Abstract:
A strong direct product theorem says that if we want to compute k independent instances of a function, using less than k times the resources needed for one instance, then our overall success probability will be exponentially small in k. We establish such theorems for the classical as well as quantum query complexity of the OR function. This implies slightly weaker direct product results for all total functions. We prove a similar result for quantum communication protocols computing k instances of the Disjointness function. Our direct product theorems imply a time-space tradeoff T2*S=Omega(N3) for sorting N items on a quantum computer, which is optimal up to polylog factors. They also give several tight time-space and communication-space tradeoffs for the problems of Boolean matrix-vector multiplication and matrix multiplication.
Holevo capacitites for qubit channels
Dominic Berry [University of Queensland]
18 August 2005 - abstract -

Abstract:
This study considers a class of qubit channels for which three states are always sufficient to achieve the Holevo capacity. For these channels it is known that there are cases where two orthogonal states are sufficient, two non-orthogonal states are required, or three states are necessary. Here a systematic theory is given which provides criteria to distinguish cases where two states are sufficient, and determine whether these two states should be orthogonal or non-orthogonal. In addition, the form of the optimal three-state ensemble is derived, and efficient methods of calculating the Holevo capacity are presented.
Fidelity between random quantum states
Karol �yczkowski [PI / Jagiellonian University]
17 August 2005 - abstract -

Abstract:
We review relevant probability measures in the space of mixed quantum states of a finite size (including Hilbert-Schmidt measure, Bures measure, and measures induced by partial tracing of random pure states of the extended system) and discuss their properties and possible applications.
Assuming that two random mixed states are generated according to one of these measures we compute average fidelity between them. Average value obtained may be used to gauge the quality of quantum information processing schemes.
Quantum Computing With Addressable Optical Lattices: Error
Travis Beals [University of California, Berkeley]
17 August 2005 - abstract -

Abstract:
Addressable optical lattices are those in which the site-to-site spacing is
sufficiently large (~ 5 um) to allow focusing of lasers onto individual lattice
sites, and thus site-specific gate operations. We present a proposal for quantum
computing with neutral atoms in such a lattice. We discuss sources of errors,
methods of correcting or avoiding those errors, and techniques for optimizing
gates.
All Quantum Adversary Methods are Equivalent
Robert �palek [CWI]
16 August 2005 - abstract -

Abstract:
The quantum adversary method is one of the most versatile lower-bound methods for quantum algorithms. We show that all known variants of this method are equal: spectral adversary [BSS03], weighted adversary [Amb03], strong weighted adversary [Zha04], and the Kolmogorov complexity adversary [LM04]. We also present a few new equivalent formulations of the method. This shows that there is essentially _one_ quantum adversary method. From our approach, all known limitations of all versions of the quantum adversary method easily follow.
Noiseless Circuits for measuring concurrence monotones
Hilary Carteret [University of Montreal]
15 August 2005 - abstract -

Abstract:
There has recently been a lot of interest in techniques for measuring the entanglement in an unknown density matrix, without first performing full state tomography. Entanglement measures are often defined in terms of unphysical maps, such as the Wootters 2-concurrence. This is defined in terms of the spectrum of $\rho\tilde{\rho},$ where the tilde operation is an anti-unitary map called the spin-flip. Previous proposed methods for measuring these quantities relied on full state tomography (which is very inefficient) or the Structural Physical Approximation (SPA) which suffers from large, state dependent errors. Since we know nothing about the density matrix by assumption, there is no way to correct for these. I will show how to construct a family of circuits that can measure the Wootters 2-concurrence for any 2-qubit state. These circuits do not require the deliberate addition of noise (unlike the SPA) and so will be exact up to experimental errors. If we get time, I can show how to generalise these sets of circuits to measure a multi-partite monotone defined on states on even numbers of qubits called the n-concurrence. These generalized circuits are also exact, and depend only on the dimension of the density matrix. If we are additionally given that the state is very nearly pure, its n-concurrence can be determined by a single circuit that scales linearly in the number of qubits, and requires only one-qubit gates and destructive c-SWAP gates. This talk is based on quant-ph/0309212 by the speaker, and some further work in progress in collaboration with Stephen S. Bullock. It is a sequel to the talk I gave last October on circuits for the partial-transpose spectrum, based on quant-ph/0309216, PRL vol.94, 040502 (2005).
Entangling power of permutations
Sibasish Ghosh [Department of Computer Science, University of York United Kingdom]
10 August 2005 - abstract -

Abstract:
The notion of entangling power of unitary matrices was introduced by Zanardi, Zalka and Faoro, where the linearized entropy of subsystem`s density matrix was used as a measure of entanglement of the density matrix of the whole system. Using the same measure of entanglement, we study the entangling power of permutations, given in terms of a combinatorial formula. We show that the permutation matrices with zero entangling power are, up to local unitaries, the indentity and the swap. We construct the permutations with the minimum nonzero entangling power for every dimension. With the use of orthogonal latin squares, we construct the permutations with the maximum entangling power for every dimension. Moreover, we show that the value obtained is maximum over all unitaries of the same dimension, with possible exception for 36. Our result enables us to construct generic examples of 4-qudits maximally entangled states for all dimensions except for 2 and 6. We numerically classify, according to their entangling power, the permutation matrices of dimension 4 and 9, and give some estimates for higher dimensions. Taking the `disentangling` power of any unitary operator, acting on a two-qudit system, as the average (over all maximally entangled states) of the linearized entropy of one subsystem of the two-qudit system which is in a state obtained after the action of the unitary operator on a maximally entangled state of the system, we show that the permutations having maximal entangling powers are also having minimal `disentangling` powers ove rthe set of all unitaries with possible exceptions for dimensions 2 and 6.
Quantum Computing With Addressable Optical Lattices: Error Characterization, Correction & Optimization
Travis Beals [University of California, Berkeley]
10 August 2005 - abstract -

Abstract:
Addressable optical lattices are those in which the site-to-site spacing is sufficiently large (~ 5 um) to allow focusing of lasers onto individual lattice sites, and thus site-specific gate operations. We present a proposal for quantum computing with neutral atoms in such a lattice. We discuss sources of errors, methods of correcting or avoiding those errors, and techniques for optimizing gates.
Bipartite subspaces having no LOCC-distinguishable bases
John Watrous [Institute for Quantum Information Science, University of Calgary]
6 April 2005 - abstract -

Abstract:
One of the focuses of the theory of quantum information in recent years has been to understand the powers and limitations of LOCC protocols, which are protocols in which two or more physically separated parties may perform arbitrary local quantum operations and may communicate with one another, but only classically. A particular problem that has been studied in this context is the state distinguishability problem: one of a known finite collection of orthogonal states is shared between two or more parties, and their goal is to determine which of the states it is by means of an LOCC protocol.

In this talk I will show that there exist subspaces of bipartite tensor product spaces with the property that no orthonormal basis of the subspace has the property that its elements can be distinguished by means of an LOCC protocol. This fact implies that there exist quantum channels having sub-optimal classical capacity even when the receiver may communicate classically with a third party that represents the channel\'s environment.
Quantum Communication Cannot Simulate a Public Coin
Dmitry Gavinsky [Institute for Quantum Information Science, University of Calgary]
17 March 2005 - abstract -

Abstract:
We study the simultaneous message passing model of communication complexity. Building on the quantum fingerprinting protocol of Buhrman et al., Yao recently showed that a large class of efficient classical public-coin protocols can be turned into efficient quantum protocols without public coin. This raises the question whether this can be done always, i.e. whether quantum communication can always replace a public coin in the SMP model. We answer this question in the negative, exhibiting a communication problem where classical communication with public coin is exponentially more efficient than quantum communication. Together with a separation in the other direction due to Bar-Yossef et al., this shows that the quantum SMP model is incomparable with the classical public-coin SMP model. In addition we give a characterization of the power of quantum fingerprinting by means of a connection to geometrical tools from machine learning, a quadratic improvement of Yao\'s simulation, and a nearly tight analysis of the Hamming distance problem from Yao\'s paper.
Exact entanglement cost for multiqubit mixed entangled states
Somshubhro Bandyopadhyay [Institute for Quantum Information Science, University of Calgary]
16 March 2005 - abstract -

Abstract:
We report the exact entanglement cost of a class of multiqubit bound entangled states, computed in the context of a universal model for multipartite state preparation. The exact amount of entanglement needed to prepare such states is determined by first obtaining lower bounds using a cut-set approach, and then providing explicit local protocols achieving the lower bound.
Complexity of graph state preparation
Mehdi Mhalla [Institute for Quantum Information Science, University of Calgary]
2 March 2005 - abstract -

Abstract:
The talk will analyse the complexity of preparation of some quantum states called graph states. We investigate the evolution of the minimal degree of a graph by a combinatorial operation introduced by Bouchet called local complementation, and characterize this minimal degree using local properties and using a game introduced by Sutner called sigma-game. Then we present a graph contraction-based algorithm that benefits of ancillary qubits to reduce the time complexity of the preparation of these states, and prove a time-space tradeoff TS=O(m), where m is the number of edges of the graph. We consider the case where unitary operators are used and also the case where only measurements are available. Finally, we prove upper and lower bounds on the size of the measurements needed when no ancillary qubits are available.
Preparation and characterization of coherent atomic superposition
Frank Vewinger [University of Kaiserslautern]
23 February 2005 - abstract -

Abstract:
The coherent control of the internal states of atoms and molecules is of increasing interest, e.g. in quantum optics, coherent control of chemical processes, quantum information processing and many more. Specifically the creation of coherent superpositions allows new possibilities in the mentioned fields. We report on the preparation of superposition states of two or more degenerate levels in a J = 2 metastable state of Neon using extensions of the STIRAP technique developed by Bergmann et al. I will discuss different schemes for the creation of two- and three-state superpositions which allow phase- and amplitude-control. Furthermore I will introduce the scheme of phase-to-population mapping, which is used to characterize coherent superposition states.
Remote Entanglement Distribution
Barry Sanders [Institute for Quantum Information Science, University of Calgary]
16 February 2005 - abstract -

Abstract:
Authors: Barry C. Sanders [Calgary] and G. Gour [UC San Diego]

Shared bipartite entanglement is a crucial shared resource for many quantum information tasks such as teleportation, entanglement swapping, and remote state preparation. In general different nodes of a quantum network share an entanglement resource, such as ebits, that are consumed during the task. In practice, generating entangled states is expensive, but here we establish a protocol by which a quantum network requires only a single supplier of entanglement to all nodes who, by judicious measurements and classical communication, provides the nodes with a unique pairwise entangled state independent of the measurement outcome. Furthermore, we extend this result to a chain of suppliers and nodes, which enables an operational interpretation of concurrence. In the special case that the supplier shares bipartite states with two nodes, and such states are pure and maximally entangled, our protocol corresponds to entanglement swapping. However, in the practical case that initial shared entanglement between suppliers and nodes involves partially entangled or mixed states, we show that general local operations and classical communication by all parties (suppliers and nodes) yields distributions of entangled states between nodes. In general a distribution of bipartite entangled states between any two nodes will include states that do not have the same entanglement; thus we name this general process remote entanglement distribution. In our terminology entanglement swapping with partially entangled states is a particular class of remote entanglement distribution protocols. Here we identify which distributions of states can or cannot be created by remote entanglement distribution. In particular we
Tackling the Challenges of Quantum Computing with Trapped Ions
Paul C. Haljan [University of Michigan]
4 January 2005 - abstract -

Abstract:
A system of laser-addressed trapped ions offers not only an attractive platform for quantum computation and simulation but also a highly controllable testbed for fundamental quantum atom optics. Our group has a three-pronged attack aiming to demonstrate the ingredients of scalable quantum computing with cadmium ions - microstructure development for scalable ion trap designs; photon-mediated entanglement together with fast entangling gates; and, finally, high fidelity phonon-mediated entanglement using ultracold ions and spin-dependent optical forces. Recent results will be presented with a focus on our progress towards implementing spin-dependent forces with optical Raman transitions. Highlights include single-ion Schroedinger cat states and our first signals of two-ion spin entanglement.

2004

The Quantum Mechanics of Hyperion and the Role of Decoherence in Classical Chaos
Nathan Wiebe [SFU]
14 December 2004 - abstract -

Abstract:
Quantum Mechanics is considered to be a more fundamental theory than classical mechanics, and as such classicality should emerge out of QM in the correct limit. The nature of this limit is still debated especially for chaotic systems. W.H. Zurek suggested that quantum mechanical corrections to Liouvilles equation cannot be ignored for chaotic bodies such as Hyperion (one of Saturns moons), and that decoherence is needed to explain the classical limit. This talk will give a brief overview of quantum and classical chaos as well as the correspondence principle. Numerical estimates of the classical limit of QM will be presented for Hyperion with and without decoherence. Finally it will be shown that contrary to Zurek, decoherence is not required to explain the classicality of Hyperion.
Cryptography with Information-theoretic Security
Hein Roehrig [University of Calgary]
23 November 2004 - abstract -

Abstract:
This will be a survey talk. Quantum cryptography is usually compared to classical complexity-based cryptography. However, information-theoretic security is also achievable in certain classical settings.
Controlling Isomerization Using Stimulated Raman Adiabatic Passage
Alex Brown [University of Alberta]
16 November 2004 - abstract -

Abstract:
Stimulated Raman adiabatic passage (STIRAP) is a powerful, strong field technique for controlling population transfer in atomic and molecular systems. In this talk, STIRAP will be introduced in the context of controlling the prototypical isomerization reaction HCN to HNC. When considering excitation processes involving the vibrational states of molecules, one must consider the high density of states that can occur. Therefore, the role that background states play in the STIRAP process will be highlighted.
Classical and quantum fingerprinting
Andrew Scott [University of Calgary]
2 November 2004 - abstract -

Abstract:
Fingerprinting enables inference of whether two messages are the same or different: each message is associated with a fingerprint and comparisons between messages are made in terms of their fingerprints alone. The number of fingerprints is always assumed less than the number of messages, leading to savings in the communication and storage of information. We derive lower bounds for the error probability when the fingerprints consist of classical information and the parties preparing the fingerprints have access to a correlated random source. When the fingerprints consist of quantum information, however, and the parties preparing the fingerprints share an entangled resource, we give protocols which achieve the same error probability with square-root fewer or less fingerprints.
Nonlocal Information in Quantum Theory
Jonathan Walgate [Institute for Quantum Information Science, University of Calgary]
2 November 2004 - abstract -

Abstract:
One of the features of quantum theory is that physical systems can store information nonlocally - without localising the data in any of their parts. This provides a new resource, and new challenges, for the study of quantum systems in general and for quantum information processing in particular. By examining simple systems that exhibit nonlocal information we can gain insight into its properties and origins.
Measurement of Geometric phase for mixed states using single photon interferometry
Marie Ericsson [University of Cambridge]
19 October 2004 - abstract -

Abstract:
Geometric phase may enable inherently fault-tolerant quantum computation. However, due to potential decoherence effects, it is important to understand how such phases arise for mixed input states. I will talk about the first experiment to measure mixed state geometric phases in optics. The experiment is performed with a Mach-Zehnder interferometer, using polarization mixed state photons that are produced in two different ways: decohering a pure state single photon with a birefringent element; and producing a nonmaximally entangled state of two photons and tracing over one of them. The mixed state geometric phase data are in very good agreement with theoretical predictions.
Noiseless Circuits for measuring entanglement
Hilary Carteret [University of Montreal]
12 October 2004 - abstract -

Abstract:
There has recently been a lot of interest in techniques for measuring the non-local properties of a density matrix as efficiently as possible. These functions are often defined in terms of unphysical maps, such as the partial transpose. Previous proposed methods for measuring these quantities relied on full state tomography (very inefficient) or the Structural Physical Approximation, which adds large amounts of noise to shift the spectrum of the partially transposed density matrix to be positive, thus incurring a corresponding loss of sensitivity. The moments of the resulting modified density operator are measured using certain sets of Mach-Zehnder interferometers and the spectrum can then be determined using a little algebra.

I will show how to construct a family of simple circuits that can determine the spectrum of the partial transpose of a density matrix, without the addition of noise. These circuits depend only on the dimension of the density matrix and do not need any components that are not already required to determine the eigenspectrum of the original density matrix by interferometry. They measure the minimum amount of information required to determine the PT-spectrum completely and they will be exact up to experimental errors.

If we get time, I can show how to measure the concurrence with a set of noiseless circuits. The concurrence also requires an unphysical operation in order to evaluate it. We must find the spectrum of $\\\\rho\\\\tilde{\\\\rho},$ where the tilde operation is an anti-unitary map. I have found a set of generalised interferometer circuits that can measure the concurrence spectrum for any two-qubit state.

This talk is based on the following pre-prints: Partial transpose circuits -- quant-ph/0309216, Concurrence circuits -- quant-ph/0309212
Quantum Interactive Proofs with Competing Provers
Gus Gutoski [Computer Science, University of Calgary]
5 October 2004 - abstract -

Abstract:
This talk introduces quantum refereed games, which are quantum interactive proof systems with two competing provers: one that tries to convince the verifier to accept and the other that tries to convince the verifier to reject. A language L is said to have a quantum refereed game if there exists a verifier that, for optimal prover strategies, correctly accepts or rejects the input with high probability.

I will show that every language having an ordinary quantum interactive proof system also has a quantum refereed game in which the verifier exchanges just one round of messages with each prover. A key part of this result proof is the fact that there exists a single quantum measurement that reliably distinguishes between mixed states chosen arbitrarily from disjoint convex sets having large minimal trace distance from one another. Time permitting, I will also show how to reduce the probability of error for some classes of quantum refereed games.
Spherical configurations, exponential sums, and quantum computation (joint work with Martin Roeteller).
Igor Shparlinski [Centre for Advanced Computing - Algorithms and Cryptography, Macquarie University Sydney (Australia)]
1 October 2004 - abstract -

Abstract:
We describe two types of vector systems on the n-dimensional sphere over C, which are useful for quantum computation. For one type, such configurations can be obtained from Gaussian sums for every prime n. Configurations of the other type are not known to exist for infinitely many n. We show that using bounds of exponential sums with polynomials one can achieve certain approximate solutions. The results are based on both the Weil and Weyl bounds and also the result of Baker-Harman-Pintz about gaps between consecutive primes.
Quantum Information Processing with Ultracold Atomic Qubits
Ivan Deutsch [Associate Professor, Regents Lecturer, Dept. of Physics and Astronomy]
1 October 2004 - abstract -

Abstract:
The end of the twentieth century saw the coming together of two of its greatest intellectual achievements -- digital information processing and quantum mechanics. What lies ahead of Moore\'s road map of ever shrinking microprocessor components is not just a tinier version of devises where switches open and close valves for classical currents, but a broad new principle based on quantum superpositions and nonlocal entanglement. In this colloquium I will review the basic principles of quantum information processing and attempts to brings these ideas to fruition in the laboratory. A particularly promising scheme employs some of the coolest matter around -- the optical lattice -- neutral atoms trapped in a virtual crystal of light.
Exact Quantum Algorithms for the Leader Election Problem
Hirotada Kobayashi [Japan Science and Technology Agency]
28 September 2004 - abstract -

Abstract:
It is well-known that no classical algorithm can solve exactly (i.e., the algorithm always halts and solves the problem with zero error) the leader election problem in anonymous networks. This work proposes two quantum algorithms that, when parties are connected by quantum communication channels, exactly solve the problem for any network topology in polynomial rounds and polynomial communication/time complexity with respect to the number of parties. This is joint work with Seiichiro Tani and Keiji Matsumoto.
Quantum error correction and multipartite entanglement
Andrew Scott [Institute for Quantum Information Science, University of Calgary]
12 August 2004 - abstract -

Abstract:
Quantum error correction negates a quantum state\'s natural susceptibility to decohere, and thus provides the long-time coherence necessary to sustain quantum computation. Beginning with a concise introduction to quantum error-correcting codes, we will investigate the integrity of a code when pushed beyond its intended capacity, presenting formulae for the probability of failure when the errors affect more qudits than that specified by the code\'s minimum distance. We then expose a connection between multipartite entanglement and quantum error-correcting codes by deriving a formula relating the weight distribution of the code to the average entanglement of encoded states.
Physical Interactions for Fast Quantum Computation
Stephen Fenner [University of South Carolina]
29 July 2004 - abstract -

Abstract:
Keeping a quantum superposition coherent during a quantum computation is one of the biggest challenges to quantum computing. If quantum computation is to be of any use, computation time must decrease relative to decoherence time. We consider the power and limits of \\\"ultrafast\\\" quantum computation, modeled by small-depth quantum circuits. To compute anything useful, these circuits must take advantage of multiqubit gates. A particularly useful multiqubit gate is the fan-out gate, which copies the classical value of a single qubit to n-1 other qubits. With fan-out, constant-depth circuits can approximate the Quantum Fourier Transform and modular arithmetic, and hence can carry out the quantum part of Shor\\\'s factoring and discrete log algorithms.

I will show that fan-out arises naturally from spin-exchange (Heisenberg) interactions. Thus in principle, one can implement these gates directly, at a cost potentally much lower than expected.
Fermionic coherent states and homodyne detection
Tomas Tyc [Institute for Quantum Information Science, University of Calgary]
12 July 2004 - abstract -

Abstract:
Coherent states of light have many useful physical and mathematical properties, e.g. they are transformed in a very simple way on a beam splitter and they factorize the correlation functions of the field to all orders.� It would be desirable to have states with similar properties for fermionic fields. It is indeed possible to define fermionic coherent states but only at the expense of going outside the Hilbert space of physical states. One can also define \"coherent states\" within the Hilbert space but their properties are by far not as useful as those of their boson counterparts. In particular, the factorization of the correlation functions turns out to be impossible. In my talk I will present the results of our recent research on this subject and will also mention the generalization of homodyne detection to fermionic fields.
Quantization of Classical Walk Based Algorithms
Mario Szegedy [Rutgers University]
9 July 2004
Nonlocal Information
Jonathan Walgate [Institute for Quantum Information Science, University of Calgary]
28 June 2004 - abstract -

Abstract:
Multipartite quantum systems can store information in the correlation of their parts, rather than in the parts themselves. This quintisentially nonclassical behaviour is most familiar in the phenomenon of entangled states. This talk explores the origin and properties of \\\"nonlocal\\\" quantum information.
Quasinormal modes: The characteristic music of black holes
Suneeta Vardarajan [University of Alberta Physics]
18 June 2004 - abstract -

Abstract:
The unique imprint of a black hole can be found in the time behaviour of perturbations of the black hole. Of particular interest is a set of complex frequencies, the quasinormal modes, that describe in part the temporal behaviour of perturbations. Quasinormal modes are interesting because they are characteristic only of the black hole and are not sensitive to the initial conditions of the perturbation. They are in some sense analogous to modes of leaky optical cavities or of musical instruments. In this talk, I describe some of my work and some exciting questions concerning quasinormal modes. I also outline a problem that has generated a lot of excitement : namely, a proposed connection between the area spectrum of a black hole in a quantum theory of gravity and the classical quasinormal mode spectrum.
Tripartite entanglement of an atom in an optical cavity
Tom Harmon [Institute for Quantum Information Science, University of Calgary]
4 June 2004 - abstract -

Abstract:
Single-atom cavity quantum electrodynamics (QED) is important at a scientific level as a testbed for atom-field coupling in combined systems and to explore atom-field entanglement, which important for tests of QED and applications to quantum information science. At a technological level, single-atom cavity QED offers the prospect of single-photon sources, quantum memory storage, and quantum computing. The theory of the atom in the cavity is well described by the Jaynes-Cummings model, which treats the atom as an electric dipole interacting with a single mode of the cavity field. However, recent progress with trapping neutral atoms and ions allows quantum features of the motion to arise. The resultant electron-photon-phonon entanglement is especially interesting as a manifestation of tripartite entanglement, which can now be investigated in cavity QED. We are particularly interested in the effect this tripartite entanglement has on the entanglement between the atom-photon system which defines the computational basis. It is shown that tripartite entanglement between all three subsystems comes at the cost of a degredation of the atom-photon entanglement.
Towards a Quantum Programming Language
Peter Selinger [University of Ottawa]
3 June 2004 - abstract -

Abstract:
In this talk, I will propose the design of a programming language for quantum computing. Traditionally, quantum algorithms are usually expressed at the hardware level, for instance in terms of the quantum circuit model or quantum Turing machines. These approaches do not encourage structured programming or abstractions such as data types. In my talk, I will describe the syntax and semantics of a simple quantum programming language with high-level features such as loops, recursive procedures, and structured data types. The language is functional in nature, statically typed, free of run-time errors, and it has an interesting denotational semantics in terms of complete partial orders of superoperators.
Continuous measurement of a solid-state charge qubit
Tom Stace [University of Cambridge]
21 May 2004 - abstract -

Abstract:
I will discuss the problem of measurement of a solid-state charge qubit, consisting of a single electron on a double well system, using a point-contact (PC) detector. In this system, inelastic processes in the PC are significant, and reduce the detection efficiency. I will also present quantum trajectory simulations of the dynamics of the system under measurement.
Faithful Teleportation with Partially Entangled States
Gilad Gour [University of Alberta]
19 May 2004
Distributed compression of quantum information
Dominic Berry [Macquarie University Department of Physics]
14 May 2004 - abstract -

Abstract:
In the usual form of quantum compression, an ensemble of pure states may be compressed to a lower average dimension. In distributed compression, the states are shared between two parties, and the compression must be performed using only local operations. In general, the compression is not as efficient in this case. In the case that the states are orthogonal product states, the compression can take full advantage of correlations between the sources, and the compression is as efficient as global compression. I will show that if the states are nonorthogonal, the compression that is possible is poorer, and no advantage can be gained from correlations between the sources.
Quantum Logic in Optical Lattices via Trap induced Shape Resonances in Controlled Atomic Collisions
Rene Stock [University of New Mexico]
12 May 2004 - abstract -

Abstract:
Controlled collisions of ultracold atoms in optical lattices provide new avenues for performing quantum logic. We analyze controlled collisions of ultracold atoms by deriving a new generalized pseudopotential which captures all the scattering properties and bound states of the true atom-atom interaction and provides an important tool in atomic collision theory . We apply this model to evaluate quantum-logic gates based on newly discovered trap induced shape resonances.
Quantum Coin Flipping Part II
Hein Roehrig [Institute for Quantum Information Science, University of Calgary]
7 May 2004
An anatomy of a quantum adiabatic algorithm that transcends Turing computability
Tien Kieu [Swinburne University of Technology, Australia]
30 April 2004 - abstract -

Abstract:
We point out [1, 2, 3] the fallacies in the common belief that Cantor¹s diagonal arguments, employed for the proof of recursive noncomputability of the Turing halting problem, could be used to further rule out all computation beyond the Turing barrier. We then present and analyse the general settings of a quantum adiabatic algorithm [4] for the Turing-noncomputable Hilbert¹s tenth problem, which is also equivalent to the Turing halting problem. The algorithm is made possible by the quantum adiabatic theorem, thanks to the exploitation of which we can impose a universal structure on suitably constructed dimensionally infinite Hilbert spaces. Our ability to erect such a structure, namely that of the spectral flows without level crossings of energy-ordered states, is in direct contrast to the structurelessness in recursive computation that has otherwise led to the Turing noncomputability of the problems under consideration. Such imposed structure and other quantum properties of coherence and tunnelling are the reasons why our quantum algorithm can probabilistically perform what seems to be an impossible task of searching through the positive integers in a finite time! More explicitly, our algorithm can probabilistically locate a particular single energy eigenstate in a dimensionally infinite Hilbert space in a finite time^Ëa task equivalent to finding a needle in an infinite haystack, but also a task obviously beyond the ability of deterministic Turing machines. [1] T. Ord and T.D. Kieu, The diagonal method and hypercomputation, to appear in British Journal for the Philosophy of Science, 2004. [3] E.S. Santos, Computability by probabilistic Turing machines, Trans. Am. Math. Soc. 159:165-184, 1971. [4] T. Ord and T.D. Kieu, Using biased coins as oracles, cs.OH/0401019, 2004. [2] T.D. Kieu, Quantum adiabatic algorithm for Hilbert\'s tenth problem: I. The algorithm, quant-ph/0310052, 2003.
Continuous-variable experiments with qubits
Alex Lvovsky [Konstanz University]
23 April 2004
Quantum Coin Flipping
Hein Roehrig [Institute for Quantum Information Science, University of Calgary]
16 April 2004 - abstract -

Abstract:
Alice and Bob want to meet. Alice would like that Bob comes to her whereas Bob prefers that Alice visits him. To flip a coin, they would have to meet; instead, they can execute a \\\"coin flipping protocol\\\" communicating over classical and/or quantum channels. This talk will be an introduction to quantum coin flipping and related problems. See also quant-ph/0304112
Decoherence, Continuous Measurement and the Quantum-Classical Transition
Shohini Ghose [Institute for Quantum Information Science, University of Calgary]
2 April 2004 - abstract -

Abstract:
This will be a review talk outlining the evolution of decoherence theory, its connection to the measurement problem and the quantum-classical transition and the main theoretical and experimental results. I will also present the quantum trajectory approach to modelling continuous measurements and unravelling the master equation that describes a system undergoing decoherence, and how the transition from classical to quantum dynamics can occur in such systems.
The Black Hole Information Loss Problem
Saurya Das [University of Lethbridge]
26 March 2004 - abstract -

Abstract:
Abstract: Black holes, which are one of the most intriguing predictions of general relativity, are not entirely black. Quantum mechanics predicts that a black hole radiates like an almost perfect black body (Hawking radiation) at a characteristic temperature (Hawking temperature). Moreover, it has entropy proportional to its horizon area. Its mass, temperature and entropy satisfy laws analogous to the laws of thermodynamics. If a black hole radiates completely due to Hawking radiation, then all information which went inside it during its formation would be lost forever (since thermal radiation carries no information about its interior). This suggests that the evolution of the black hole is non-unitary, in which pure states evolve to mixed states. All proposed fundamental theories of quantum gravity (including string theory and loop quantum gravity), which should describe the microscopic details of this evaporation, are however unitary. This apparent paradox, known as the `Black Hole Information Loss Problem\\\\\\\', will be reviewed in this talk, along with some proposed resolutions.

Reference: S. Das, hep-th/0403202
Quantum and Classical Strong Direct Product Theorems and Optimal Time-Space Tradeoffs
Hartmut Klauck [Institute for Quantum Information Science, University of Calgary]
19 March 2004 - abstract -

Abstract:
A strong direct product theorem says that if we want to compute k independent instances of a function, using less than k times the resources needed for one instance, then our overall success probability will be exponentially small in k. We establish such theorems for the classical as well as quantum query complexity of the OR function. This implies slightly weaker direct product results for all total functions. We prove a similar result for quantum communication protocols computing k instances of the Disjointness function.

Our direct product theorems imply a time-space tradeoff T^2S=Omega(N^3) for sorting N items on a quantum computer, which is optimal up to polylog factors. They also give several tight communication-space and time-space tradeoffs for the problems of Boolean matrix-vector multiplication and matrix multiplication.

Joint work with Ronald de Wolf and Robert Spalek. There\'s a paper under quant-ph/0402123.
Weak Continuous Measurements of Superconducting Quantum Bits
Anatoly Smirnov [D-Wave Systems Inc., Vancouver, B.C.]
10 March 2004
Quantum fingerprinting
Rolf Horn [Institute for Quantum Information Science, University of Calgary]
5 March 2004
Berry phase in open systems
Peter Marzlin [Institute for Quantum Information Science, University of Calgary]
27 February 2004
On the Number of Copies Required for Entanglement Distillation Part II
John Watrous [University of Calgary Computer Science]
13 February 2004
On the Number of Copies Required for Entanglement Distillation Part I
John Watrous [University of Calgary Computer Science]
6 February 2004

2003

Quantum Error Correcting Codes and The Security of BB84 Part III
Richard Cannings [University of Calgary Computer Science]
4 December 2003 - abstract -

Abstract:
This is the final lecture of the security proof of BB84. In this lecture, we slightly alter the general entanglement purification protocol, and then prove that it is a secure quantum key distribution (QKD) protocol called the Modified Lo--Chau QKD. Finally, we reduce the Modified Lo--Chau QKD to BB84 by a series of simple reductions.
Quantum Error Correcting Codes and The Security of BB84 Part II
Richard Cannings [University of Calgary Computer Science]
27 November 2003 - abstract -

Abstract:
BB84 is a quantum key distribution protocol that allows two parties to generate an unbreakable secret key. This is a very important protocol in both quantum information science and cryptography because BB84 has unparalleled security and it appears close to being physically realizable. It took over 12 years to prove the security of BB84, and even then, the proofs were complicated and only understood by few. In 2000, Shor and Preskill published a simplified proof of security for BB84 based on properties of CSS quantum error correcting codes. In this two part tutorial, we follow the Shor-Preskill proof (quant-ph/0003004) and introduce necessary background material.

In the second lecture, we discuss quantum versions of some topics discussed in the first lecture. Namely,
- CSS quantum error correcting codes,
- entanglement purification, and
- the unconditional security of BB84.
Quantum Error Correcting Codes and The Security of BB84 Part I
Richard Cannings [University of Calgary Computer Science]
20 November 2003 - abstract -

Abstract:
BB84 is a quantum key distribution protocol that allows two parties to generate an unbreakable secret key. This is a very important protocol in both quantum information science and cryptography because BB84 has unparalleled security and it appears close to being physically realizable. It took over 12 years to prove the security of BB84, and even then, the proofs were complicated and only understood by few. In 2000, Shor and Preskill published a simplified proof of security for BB84 based on properties of CSS quantum error correcting codes. In this two part tutorial, we follow the Shor-Preskill proof (quant-ph/0003004) and introduce necessary background material.

BB84 is a quantum key distribution protocol that allows two parties to generate an unbreakable secret key. This is a very important protocol in both quantum information science and cryptography because BB84 has unparalleled security and it appears close to being physically realizable. It took over 12 years to prove the security of BB84, and even then, the proofs were complicated and only understood by few. In 2000, Shor and Preskill published a simplified proof of security for BB84 based on properties of CSS quantum error correcting codes. In this two part tutorial, we follow the Shor-Preskill proof (quant-ph/0003004) and introduce necessary background material.

In the first lecture, we discuss
- BB84
- classical error correcting codes,
- the random sample test,
- correlation purification, and
- a practical variant of BB84.
Einstein meets Schrodinger: The sequel
David Hobill [University of Calgary Physics and Astronomy]
13 November 2003 - abstract -

Abstract:
The Lorentz covariance of special relativity places restrictions and relationships (that do not exist in non-relativistic theories) on the dynamical variables describing the state of a physical system. This is true for both classical and quantum mechanics.

In relativistic quantum theory a quantum observable must be coupled to the four-momentum of the particle carrying the quantum information. The Lorentz transformations act directly on the momentum of the particle and as a result induce unitary transformations on the other (secondary) quantum variables. In the case of the particle spin this transformation is known as a Wigner rotation.

A simple example will be analyzed for a system consisting of two 1/2 spin particles entangled into an EPR pair. It will be shown that spin measurements made by two moving observers will find a new form of ``entanglement\'\' arising between the spin and momentum degrees of freedom and that the anti-correlation that exists in the non-relativistic case is modified so that it depends on the motion of both the particles and the observers. This will have implications in any form of quantum communication involving the motion of particles and observers.
A Primer on Relativity for Quantum Information Scientists
David Hobill [University of Calgary Physics and Astronomy]
6 November 2003 - abstract -

Abstract:
The theories of quantum mechanics and relativity are two fundamental theories of physics that have had a most profound influence about how we view the world around us. Since relativity is a theory of the structure of spacetime and quantum mechanics is a theory of the structure of matter, one would expect that there should be an overall theory uniting the two. However the two theories have coexisted for nearly a century in an uneasy relationship.

This seminar will introduce some of the essential ideas of relativity theory and will then go on to discuss some of the issues concerning the need to understand quantum information processes from a relativistic point of view.
Improving single photon sources via linear optics and photodetection
Dominic Berry [Macquarie University Department of Physics]
30 October 2003 - abstract -

Abstract:
Many quantum information applications rely on the production of a single photon. In practice, single photons are generated with non-unit efficiency; that is, the actual state is a mixture of vacuum with a single photon. In order to obtain a high probability of a single photon, one may attempt to improve the source, or perform post-processing of the source to improve the efficiency. A promising method of performing post-processing is via linear optics and photodetection. I will present results showing that it is possible to improve the probability of a single photon using this method, and examine the limits to this method.
Rapid Data Search Using Adiabatic Quantum Computation
Saurya Das [University of Lethbridge]
23 October 2003 - abstract -

Abstract:
We show that in Adiabatic Quantum Computation, a suitable choice of time-dependent Hamiltonian can considerably speed up the search for a marked item in an unstructured database (of size N). Consequently, the item can be found in a time much less than O(sqrt(N)), required by previous algorithms. The price to pay is that in intermediate stages of the computation process, the ground state energy of the computer increases to large values, although it returns to zero at the end of the process. We give specific examples of such Hamiltonians and propose ways to keep the intermediate energy low.

REFERENCES: (1) S. Das, R. Kobes, G. Kunstatter, J. Phys. A: Math. Gen. 36 (2003) 1-7 [quant-ph/0204044]. (2) D. Ahrensmeier, S. Das, R. Kobes, G. Kunstatter, H. Zaraket, Proc. of QCMC-02, MIT [quant-ph./0208107].
Quantum Fourier Transforms and Integer Multiplication
Graeme Ahokas [University of Calgary Computer Science]
16 October 2003 - abstract -

Abstract:
The quantum Fourier transform (QFT) is a key ingredient in many quantum algorithms. In this talk we present efficient circuit constructions for both the exact and approximate QFT, and relate the difficulty of computing the QFT to classical integer multiplication.
The Quantum to Classical Transition in Coupled Systems
Shohini Ghose [Institute for Quantum Information Science, University of Calgary]
9 October 2003 - abstract -
One qubit vs. one bit fingerprinting schemes
Niel de Beaudrap [University of Calgary Computer Science]
3 October 2003 - abstract -

Abstract:
Fingerprinting is a technique in communication complexity in which two parties (Alice and Bob) with large data sets send short messages to a third party (a referee), who attempts to determine whether these data sets are equal. In this talk, we consider the extreme scenario of performing fingerprinting where Alice and Bob both send either one bit (classically) or one qubit (in the quantum regime) messages to the referee. Restrictive bounds are demonstrated for the error probability of one-bit fingerprinting schemes, and show that it is easy to construct one-qubit fingerprinting schemes which can outperform any one-bit fingerprinting scheme. It is hoped that this analysis will provide results useful for performing physical experiments, which may help to advance implementations for more general quantum communication protocols.