Storing short single-photon-level optical pulses in Bose–Einstein condensates for high-performance quantum memory

Abstract

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.

Topical White Paper: A Case for Quantum Memories in Space

“…Even though the setups required to laser cool atomic ensembles are relatively more complex than the ones implemented for warm vapours, the lower temperatures of a cold atom cloud inhibits thermal diffusion and grants long coherence times. Of particular interest is photon storage in ultracold quantum gases such as Bose-Einstein condensates [49][50][51]: not only does the reduction of thermal motion offer long storage times, but the large optical depth allows for high write-read efficiency and the refined state preparation increases the fidelity of the storage in the atomic spin state. In the past years optical memory has been demonstrated in these systems achieving high efficiencies [9,52], long storage time [53], and temporal [52,54] and spatial multiplexing [55,56].…”

Superradiance-Mediated Photon Storage for Broadband Quantum Memory

“…Additional NDFs (providing up to 38 dB attenuation) are placed behind the MOT cell along the probeoutput-path so that the average number of photons effectively reaching the SPD is below 1 (≈ 0.5-0.7) thereby preventing the detector from going into the saturation (since nin ∼ 10 3 ). We calibrate nin by measuring probe counts in the absence of atomic cloud, following the procedure in our earlier studies [41,43,44] Broadband memory demonstrations require strong control fields and so operation at the single-photon-level warrants heavy filtering of the scattered control light which would otherwise leak into the probe channel and produce spurious detection counts. In our current setup, the spatial mode of control field is separated from the probe by θ = 5 • .…”

“…We note that the control noise preventing single-photon-level operation is purely technical and not generated by the memory processes (unlike four-wave-mixing noise). In future implementations, this scattered leak can be eliminated by setting a larger separation angle between probe and control fields [43,44].…”

“…This would demand a square-shaped π-control with duration T C = 1 10 T SR = 0.11 ns and Rabi frequency Ω opt C /2π = 4.5 GHz. Finally, we make a performance comparison (efficiency, optical depth, bandwidth, and control-power) between SR and other memory approaches, including Autler-Townes-Splitting (ATS) [41][42][43][44] and electromagneticallyinduced-transparency (EIT) [45][46][47], which are examples of non-adiabatic and adiabatic protocols, respectively. We base this comparison on the adiabaticity parameter, corresponding to T P dγ = 2 (SR); T P dγ = 14 (ATS); and T P dγ = 60 (EIT), for a broadband, exponential probe with T P 1/γ.…”

Engineering atomic polarization with microwave-assisted optical pumping

“…As a platform for quantum technologies, alkali-metal atomic ensembles, which naturally support microwave and optical transitions, provide a good opportunity for microwave-to-optical quantum transduction [4][5][6][7][8][9] and for storing and retrieving quantum information on demand [10][11][12]. The nonlinear effects of microwave interactions on optical properties of alkali vapors also include the transduction of classical signals [13][14][15][16][17][18][19][20][21][22][23], compact atomic clocks [24][25][26], microwave electrometry [27], and static and microwave magnetometry [28][29][30][31][32].…”