Photon-Echo quantum memory and controlled state manipulation

Quantum memories, as a part of a quantum repeater, are key elements to extend quantum communication beyond its current distance limit of around 100 km. In addition to memories, quantum repeaters also require the distribution of entangled photons as well as state manipulation, which is generally accomplished by means of interferometric optical setups. We experimentally investigate a novel approach based on photon-echo type atom light-interaction that allows combining storage with controlled transformation of quantum states [1,2]. As an example, we perform a proof-of-principle demonstration of unambiguous state discrimination in an Er:LiNbO3 waveguides cooled to 3K using states encoded into pulses of light in superposition of different temporal modes. Our approach can easily be extended to any unitary transformation. The high robustness and flexibility compared to current optical setups for state manipulation makes it promising for quantum communication and computation protocols that require storage and manipulation of photons, in particular quantum repeaters.