Future quantum photonic networks require coherent optical memories, preferably operating at room temperature, for synchronizing quantum sources and gates of probabilistic nature. Until now, however, room-temperature atomic memories have suffered from an intrinsic read-out noise. Here we demonstrate a fast ladder memory (FLAME) mapping the optical field onto the superposition between electronic orbitals of rubidium vapor. Employing a ladder level-system of orbital transitions with nearly degenerate frequencies simultaneously enables high bandwidth, low noise, and long memory lifetime. We store and retrieve 1.7-ns-long pulses, containing 0.5 photons on average, and observe short-time external efficiency of 25%, memory lifetime (1/e) of 86 ns, and below 10⁻⁴ added noise photons. Consequently, coupling this memory to a probabilistic source would enhance the on-demand photon generation probability by a factor of 12, the highest number yet reported for a noise-free, room-temperature memory. This paves the way towards the controlled production of large quantum states of light from probabilistic photon sources.

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E. Poem, R. Finkelstein, O. Michel, O. Lahad, and O. Firstenberg, "Fast, noise-free memory for photon synchronization at room temperature," Proc. SPIE 10771, Quantum Communications and Quantum Imaging XVI, 107710A (Presented at SPIE Optical Engineering + Applications: August 19, 2018; Published: 18 September 2018); https://doi.org/10.1117/12.2320508.