Abstract
Quantum memories are essential for quantum information processing. Techniques have been developed for quantum memory based on atomic ensembles. The atomic memories through optical resonance usually suffer from the narrow-band limitation. The far off-resonant Raman process is a promising candidate for atomic memories due to broad bandwidths and high speeds. However, to date, the low memory efficiency remains an unsolved bottleneck. Here, we demonstrate a high-performance atomic Raman memory in 87Rb vapour with the development of an optimal control technique. A memory efficiency of above 82.0% for 6 ns~20 ns optical pulses is achieved. In particular, an unconditional fidelity of up to 98.0%, significantly exceeding the no-cloning limit, is obtained with the tomography reconstruction for a single-photon level coherent input. Our work marks an important advance of atomic memory towards practical applications in quantum information processing.
Highlights
Quantum memories are essential for quantum information processing
Our Raman memory starts with a large ensemble of atoms that were initially prepared in the |m〉 = | 52S1/2, F = 2〉 state by a 44-μs-long optical pumping pulse (OP)
The two strong driving beams, W and R, can be generated by the same or different semiconductor lasers (Toptica, DLPro + Boosta) and are coupled into the same single-mode fiber. Their intensities and temporal shapes are controlled by acousto-optic modulators (AOMs)
Summary
Quantum memories are essential for quantum information processing. Techniques have been developed for quantum memory based on atomic ensembles. Polzik’s group[12] demonstrated a quantum memory with a fidelity of 70% based on the off-resonant Faraday effect These examples[12,20,21] successfully demonstrated the capability to store optical states with high efficiency and/or fidelity exceeding the classical limit[22,23,24] and sub-megahertz bandwidths. Quantum sources with bandwidth at the GHz level have been used in long-distance quantum communication[26,27] and quantum computers[28] Unlike these protocols, far-off-resonant atomic Raman memory can store short-time pulses corresponding to high bandwidths and can operate at high speeds.
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