Scalable Linear-Cavity Enhanced Quantum Memory

Coherent storage and retrieval of single photons in a quantum memory enables scalable growth of photonic entangled states via linear optics. The resulting increase in power of photonic quantum computers will unlock new applications on the pathway to fault tolerance. Quantum memories based on off-resonant cascaded absorption (ORCA) in rubidium vapour allow this storage to be broadband, noise-free, and high efficiency. Through algorithmic pulse-shape optimisation, we have previously demonstrated single-pass memory efficiency of almost 90\%. Here, we implement a cavity-enhanced GHz-bandwidth ORCA memory with smaller footprint and reduced power requirements compared to conventional single-pass schemes. By combining a strong magnetic field with polarisation control, we maintain a Doppler-free two-photon interaction and eliminate the need for optical pumping. The performance provided by the cavity establishes the feasibility of large arrays of ultra-compact, high-efficiency, room-temperature quantum memories, while the low control power requirements highlight a route to single-photon-level nonlinearities.