Abstract
Quantum interfaces between photons and atomic ensembles have emerged as powerful tools for quantum technologies. Efficient storage and retrieval of single photons requires long-lived collective atomic states, which is typically achieved with immobilized atoms. Thermal atomic vapours, which present a simple and scalable resource, have only been used for continuous variable processing or for discrete variable processing on short timescales where atomic motion is negligible. Here we develop a theory based on motional averaging to enable room temperature discrete variable quantum memories and coherent single-photon sources. We demonstrate the feasibility of this approach to scalable quantum memories with a proof-of-principle experiment with room temperature atoms contained in microcells with spin-protecting coating, placed inside an optical cavity. The experimental conditions correspond to a few photons per pulse and a long coherence time of the forward scattered photons is demonstrated, which is the essential feature of the motional averaging.
Highlights
Quantum interfaces between photons and atomic ensembles have emerged as powerful tools for quantum technologies
The averaging thereby removes the detrimental effect of atomic motion for continuous variable quantum information processing, where a specific optical mode is measured by homodyne detection[14,15,16]
As opposed to previous ensemble-based experiments with discrete variables encoded in moving atoms[23], which typically rely on performing operations sufficiently fast that the atoms remain inside the laser beams, we show how a form of motional averaging similar to the one used for continuous variable processing can be used to erase the which atom information
Summary
Evaluating the correlation including the Doppler shift, we find that the decay of the correlations are approximately exponential such that, for example, hgjð0ÞgjðtÞi1⁄4hgjð0Þ2ie À Gt þ hgjð0Þi2ð1 À e À GtÞ, where the first term contains the short-time correlations, while the second term characterizes the long-time limit where the correlations are only through the average values Employing this model for the atomic correlations and assuming the effective interaction time (1/k2) is set by the linewidth of the filter cavity, we find. The idea of the motional averaging is to use a spectrally narrow filter cavity to select only the photons emitted in the narrow coherent peak Since this narrow peak corresponds to a long interaction time, this means that all atoms participate in the resulting spin wave. This error is equal to the probability E that an atom is in the wrong state
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