Quantum-memory spin-wave processor: multiplexed generation, programmable interference and detection

Multiplexing stands at the core of modern optical communication, and it is also expected it will be highly beneficial, if not essential, for quantum communication with photons. Multiplexed quantum memories are then required to serve as quantum repeater nodes. We present a quantum memory based on a cold atomic ensemble that uses multiplexing of wavevectors (i.e. both angles of emission and storage times, combining spatial and temporal multiplexing) for the quasi-deterministic generation of single photons. Inside the memory, the photons can be stored in the form of spatially-extended spin waves, the phase of which can be modified via an ac-Stark shift protocol with spatial resolution. This allows us to experimentally implement linear-optical operations in the spin-wave domain, in particular demonstrating the Hong-Ou-Mandel interference for the pairs of collective spin-wave excitations. We envisage that such simple yet universal operations inside the memory can serve for optimizing the performance of the memory in the context of quantum repeaters, by implementing error-correction schemes in the memory. 

In the presentation I would like to introduce how we optimize the capacity of the memory with proper atomic, optical and camera-based detection systems design, achieving a capacity of 2000 independent modes. With this, I will present the protocols for processing and interfering spin waves and generating single photons and Bell states demonstrated so far, and envisage the near-term new capabilities.