# Single-photon-level light storage in cold atoms using the Autler-Townes splitting protocol. (arXiv:1905.05856v1 [quant-ph])

Broadband spin-photon interfaces for long-lived storage of photonic quantum
states are key elements for quantum information technologies. Yet, reliable
operation of such memories in the quantum regime is challenging due to photonic
noise arising from technical and/or fundamental limitations in the
storage-and-recall processes controlled by strong electromagnetic fields. Here,
we experimentally implement a single-photon-level spin-wave memory in a
laser-cooled Rubidium gas, based on the recently proposed Autler-Townes
splitting (ATS) protocol. We demonstrate storage of 20-ns-long laser pulses,
each containing an average of 0.1 photons, for 200 ns with an efficiency of
$12.5\%$ and signal-to-noise ratio above 30. Notably, the robustness of ATS
spin-wave memory against motional dephasing allows for an all-spatial filtering
of the control-field noise, yielding an ultra-low unconditional noise
probability of $3.3\times10^{-4}$, without the complexity of spectral
filtering. These results highlight that broadband ATS memory in ultracold atoms
is a preeminent option for storing quantum light.