Abstract
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.
Highlights
Broadband spin-photon interfaces for the long-lived storage of photonic quantum states are key elements for quantum information technologies
Interfacing nonclassical light with these memories is necessary, but has proven to be difficult for two reasons: the substantial mismatch between the inherently large bandwidth of quantum light and the narrow acceptance bandwidth of well-studied atomic memories, and the unfaithful storage and recall processes due to photonic noise introduced by memory itself, which may degrade or fully destroy the quantum nature of the stored light
The controlled reversible inhomogeneous broadening (CRIB) [7,8] and gradient echo memory (GEM) [9,10] are widely studied protocols that rely upon the absorption of light via artificially broadened spectral features controlled by external electric or magnetic field gradients
Summary
Broadband spin-photon interfaces for the long-lived storage of photonic quantum states are key elements for quantum information technologies. The efficient storage of sub-ns pulses (GHz bandwidths) in these systems is technically very demanding in terms of optical depth and coupling-field power, due to the inherent adiabatic operation of the Raman protocol, which exhibits unfavorable bandwidth scaling compared to fast memory protocols [23,31].
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