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 × 10 −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.For large-scale quantum networks to become practical, storage and on-demand recall of photonic quantum states must be available at timescales of up to several milliseconds [1,2]. Interfacing non-classical 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 (from most popular single-photon sources) 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 quantum nature of the stored light. This noise is particularly problematic with on-demand memories that require control electromagnetic fields, and is typically much more detrimental for broadband implementations [3][4][5].A promising approach to noise-free broadband memory is a family of photon-echo-based protocols that feature inherently fast (non-adiabatic) memory operation [6]. 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. However, implementing a broadband CRIB or GEM memory is technically challenging due to the infeasibility of large field gradients with rapid switching times. The atomic frequency comb (AFC) technique offers a solution to this limitation, as this approach relies on tailoring a comb-shaped spectral feature for light absorption without needing controlled broadening [11]. To this end, broadband AFC quantum memories have been successfully demonstrated for high-fidelity storage of entangled photons in the GHz-bandwidth regime using ensemble of two-level rare-earth (RE) ions in solids [12][13][14][15]. But, intrinsically short and pre-programmed storage times in these memories restrict their us...
Large-scale quantum networks require quantum memories featuring long-lived storage of non-classical light together with efficient, high-speed and reliable operation. The concurrent realization of these features is challenging due to inherent limitations of matter platforms and light–matter interaction protocols. Here, we propose an approach to overcome this obstacle, based on the implementation of the Autler–Townes-splitting (ATS) quantum-memory protocol on Bose–Einstein condensate (BEC) platform. We demonstrate a proof-of-principle of this approach by storing short pulses of single-photon-level light as a collective spin-excitation in a rubidium-BEC. For 20 ns long-pulses, we achieve an ultra-low-noise memory with an efficiency of 30% and lifetime of 15 μs. The non-adiabatic character of the ATS protocol (leading to high-speed and low-noise operation) in combination with the intrinsically large atomic densities and ultra-low temperatures of the BEC platform (offering highly efficient and long-lived storage) opens up a new avenue toward high-performance quantum memories.
Using cold and ultracold rubidium atoms controlled with lasers intense enough to put the system into the Autler-Townes regime, fast, efficient, and broadband storage and manipulation of photonic signals is achieved. In demonstrating single-photon-level operation, signals are read out with exceptionally low-noise, which is inherent to this method. Finally, high efficiency and longer storage times are made possible by using Bose-condensed samples as the storage medium.
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