Quantum photonics: From fundamental quantum science to the gravity interface - Philip Walther

In recent decades, quantum photonics has emerged as a powerful platform for exploring fundamental questions in quantum physics. In this talk, I will present our work on quantum causality, where we experimentally realize superpositions of different orders of operations. This approach enables novel, non-standard quantum computing architectures, as well as deterministic protocols for reversing qubit evolution.
Quantum light also provides new opportunities for precision measurements. In particular, quantum interferometry has developed into a key tool for achieving ultrasensitive detection beyond classical limits. Beyond practical applications, such techniques offer a route to probing fundamental physical effects in the laboratory. A prominent open question is how gravity influences quantum entanglement-an issue at the heart of the interplay between quantum mechanics and general relativity.
I will present a major step in this direction: a high-precision Sagnac quantum optical interferometer capable of measuring Earth's rotation. By exploiting maximally path-entangled two-photon states, we observe super-resolution in the rotation signal.
Finally, I will outline our ongoing efforts to experimentally probe the interface between quantum mechanics and gravity using entangled photon states. These experiments aim to employ interferometers with paths subjected to different gravitational potentials, paving the way toward laboratory tests of quantum effects in curved spacetime.