利用连续变量三色偏振纠缠态开展量子存储和长距离量子态传输的理论和实验研究

Quantum networks have become an advanced topic in quantum information because of their high efficiency and security. Quantum memory is the basis of long-distance quantum communications and quantum computation, the interaction between optical field and multi-level atoms is one of the typical and effective means to realize quantum memory. To construct a practical quantum network, non-classical state light field which can be matched with quantum nodes need to be prepared, firstly. The polarization entangled state described by Stokes operators can easily correspond to the atomic spin operators, which also has simple measurement and could easily realize the interaction between the light and atoms. Therefore, multi-color polarization entangled states which consisting of optical sub-modes at fiber transmission and atomic transition frequencies are ideal information carriers for quantum network research. According to the reasons above, the three-color polarization entangled state with optical parameter conversion would be obtained first in our project. Afterwards, the polarization entangled state will be used as information carrier to realize efficient and stable quantum memory in cesium atomic ensemble and efficient transmission of the quantum state in two 6 km fiber channels, simultaneously. Finally, the deterministic quantum entanglement that above 3 dB between the atomic ensemble and multiple fiber channels will be established. We hope the protocol could be integrated with the existing urban optical fiber communication networks to provide a theoretical and experimental reference for building the practical quantum networks.

量子网络因其高效性和安全性而受到广泛关注，量子信息存储是实现量子信息远距离传递和量子计算的基础，而利用光场与多能级原子相互作用是一种实现量子信息存储的典型和有效手段。构造实用化量子网络，首先需制备能与量子节点匹配的非经典光场，这其中由Stokes算符描述的偏振纠缠态光场的量子起伏可以方便的和原子自旋波起伏相对应，且其测量方式简单；而多色偏振纠缠可同时与原子系统以及通信波段光纤相匹配，故多色偏振纠缠光场是开展量子网络研究的理想信息载体。因此我们拟首先在实验上利用光学参量过程获得三色偏振纠缠态光场，其次利用其作为信息载体实现连续变量偏振纠缠态在铯原子系综内高效稳定量子存储以及在两条六千米光纤通道中高效传输，继而在原子系综与两条光纤通道输出光场之间建立不低于3dB的确定性的量子纠缠，在此基础上拟利用现有城域光纤网络开展连续变量量子通信网络的研究，为连续变量量子网络实用化提供理论和实验参考。

目前，量子网络成为一个热门研究方向。利用光与多能级原子相互作用是实现量子信息存储的典型和有效手段之一，其不仅可实现多种非经典光场的量子存储，而且还能实现多个空间分离原子系综之间确定性的纠缠建立，进而实现量子信息在不同量子节点进行传输和处理。本研究拟开展基于量子存储及量子网络构建的理论及实验相关研究。偏振态光场具有测量方式简单，不需在测量端引入强本底光，适合在光纤网络中进行远距离传输；其次光场的偏振分量易与原子自旋均使用Stokes分量来描述，易于实现光场量子起伏与原子自旋波起伏的相互匹配，因而偏振态光场在量子存储以及量子信息网络构建中受到广泛关注。通过该项目资助我们首先开展了：1. 四组份偏振纠缠态远距分发的理论研究，利用连续变量偏振纠缠态光场可实现在光纤量子网络中，甚至在现有城域光纤通信网络中进行远距离纠缠分发，继而构建不同量子节点间的确定性量子关联，这对于简化量子网络结构，推进量子网络实用化具有重要研究意义（Opt. Express 30, 4, 6388, 2022）。2. 开展了用于高精度光学谐振腔和光学位相锁定的高信噪比低噪声自举放大光电探测器的研究，我们研制了一种基于标准跨阻放大电路和两级自举放大电路结合的自举低噪声光电探测器，可用于弱光条件下激光稳频和光场位相锁定,通过自举阻抗增强技术有效减小了光电二极管大的结电容的影响，显著提高了探测器的信噪比，结果表明，光信号为800uW时，研制的探测器在分析频率3MHz处，探测器的信噪比高达26.7dB，目前处于国际最先进水平( Opt. Express 30, 47826, 2022）。3. 开展了基于腔增强的热原子量子存储研究，直接测量存储效率高达67 ± 1%，同时达到接近量子噪声极限的噪声水平（Nature Communicaions 13, 2368, 2022）。4.对EIT机制实现光模的单光子、压缩态、纠缠光子对和多部纠缠态的存储和释放进行了综述研究（ADVANCES Quantum Technologies, 4, 2100071, 2021；ADVANCES IN PHYSICS: X 7，2060133， 2022）。5. 相互测试的源-器件无关的量子随机数发生器QRNG研究（Photonics Research, 10, 654, 2022）。