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中国物理学会期刊

冷原子系综中光纤腔增强且高保真度的光学存储

CSTR: 32037.14.aps.72.20222178

Fiber-cavity enhanced and high-fidelity optical memory in cold atom ensemble

CSTR: 32037.14.aps.72.20222178
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  • 利用原子系综中的Duan-Lukin-Cirac-Zoller (DLCZ)过程可产生光与原子记忆(自旋波)量子纠缠, 该纠缠可作为量子中继的重要元件. 随着量子信息研究的深入发展, 人们对量子信息存储其灵活多样性、可控性等方面提出更高的要求. 本文在冷原子系综中演示了一种基于DLCZ过程的光纤腔增强且高保真度的光学存储方案, 即将87Rb原子系综放于设计的光纤腔中, 通过光纤腔增强“写出”和“读出”光子与原子系综的耦合实现自旋波量子信息的有效恢复, 同时具有较高的保真度. 观察到有腔且锁定的情况下斯托克斯光子产生概率比无腔时增加4.6倍, 原子自旋波读出效率增加1.6倍, 实验实现22%的读出效率并具有92%的量子态保真度, 该读出效率对应一个40%的本质读出效率. 这种高度可恢复、高量子态保真度的原子-光子纠缠源, 可为未来长距离量子通信及广域大规模量子网络构建的实现提供另一种有效的途径.

     

    Entanglement between a photon and an atomic memory is an important tool for quantum repeater research. By using the Duan-Lukin-Cirac-Zoller (DLCZ) process in the atomic ensemble, quantum entanglement between a photon and an atomic spin-wave memory is produced. With the further development of quantum information, it is necessary to put forward higher requirements for the diversity and controllability of quantum memory. In this work, we experimentally demonstrate an optical memory in cold atomic ensemble with enhanced fiber-cavity and high-fidelity optical memory for the first time. We design a fiber cavity to enhance the coupling strength between light and atomic ensemble and then improve the optical retrieval efficiency. Unfortunately, the use of fiber cavity may lead to the decrease of fidelity. Therefore, it is vital to realize high fidelity in the enhanced fiber-cavity optical memory. The cavity has a round-trip length of 1.5 m and a free spectral range of 190 MHz. The finesse (F) of the cavity with the cold atoms in the DLCZ condition is measured to be \sim 18. In cavity-enhanced DLCZ scheme, we use a fiber cavity instead of a stationary cavity. If a stationary cavity is used, the signal light will be reflected by the end mirror of the cavity and then pass back through the atoms. The storage of the backward signal light will generate a short-wavelength spin wave and then lead to a rapid decoherence of the memory. When cavity is locked by using the PDH frequency locking technique, we observe that the production probability of the Stokes photons is increased by 4.6 times higher than that without cavity and retrieval efficiency of atomic spin wave is increased by 1.6 times that without cavity due to the optical cavity enhancement effect. The presented cavity-enhanced storage shows that the retrieval efficiency is \sim 22%, corresponding to an intrinsic retrieval efficiency of \sim 40%, at the same time the fidelity of the quantum state is \sim 92%. The accomplishment of this project will provide another effective way of realizing long-distance quantum communication and large-scale quantum network construction.

     

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