基于原子系综的连续变量二阶轨道角动量纠缠制备和传输的实验研究

Quantum entanglement has potential applications in quantum communication networks and quantum computing as the fundamental resource of quantum information processing. With the continuous expansion of quantum communication networks and the increasing complexity of quantum computing, the researches of multidimensional, multipartite entanglement and entanglement with multi degrees of freedom have attracted increasing interest. Continuous-variable (CV) orbital angular momentum entanglement with its special degree of freedom plays a significant role in high-dimensional quantum communication and high-capacity information networks. In the practical quantum communication networks, the quantum entanglement is quite fragile and could be easily distorted due to environment-induced decoherence, which makes the realization of long-distance transmission for the CV high-dimensional entanglement challenging. In this project, we plan to engineer CV second-order orbital angular momentum entanglement by using a four-wave mixing without a cavity based on atomic ensembles, and explore the decoherence characteristics of this entanglement in lossy channel. Furthermore, the phase-sensitive amplifier based on atomic ensembles is appointed to counteract quantum decoherence caused by transmission losses. Our research will pave the way to the development of long-distance, high-capacity quantum information networks.

量子纠缠作为量子信息处理的基本资源，在量子通信网络和量子计算领域有潜在的应用前景。随着量子通信网络的不断扩大和量子计算复杂程度的不断提高，多维度、多组份以及多自由度纠缠态的研究引起越来越多的关注。连续变量轨道角动量纠缠作为一种特殊自由度的纠缠光源，是实现高维度量子通信、构建高容量信息网络的重要资源。在实用化的量子通信网络中，外界环境会导致量子纠缠态在传输过程中的退相干。因此，实现远距离的连续变量高维纠缠态传输是一个具有挑战性的课题。本项目拟采用无腔限制的铯原子系综四波混频系统制备连续变量二阶轨道角动量纠缠态光场，研究该纠缠态光场在损耗信道中传输的退相干特性。在此基础上，利用原子系综相敏放大器对抗传输过程中损耗引起的退相干。该项目将进一步推动远距离、高容量量子信息网络的发展。

连续变量量子体系具有确定性产生、高效率量子探测、与经典通信系统兼容性好等优势，基于连续变量的量子导引、量子纠缠、量子失谐以及量子相干性是实现量子计算、量子通信和量子精密测量的重要量子资源。轨道角动量复用为各种量子通信协议提供了一种高效、高容量信息传输的有效方法。在实用化的量子通信网络中，外界环境会导致连续变量量子资源在传输过程中的退相干，实现远距离的连续变量高维量子资源传输是一个具有挑战性的课题。.本项目基于无腔限制的铯原子系综四波混频系统实验制备了纠缠度约为-3.3 dB的l=0;1;2阶轨道角动量连续变量纠缠态光场，证明热碱金属原子系综双Λ型能级结构四波混频系统具有空间多模的优势，可以用于制备高阶、多维度轨道角动量纠缠态；理论和实验证明了l=1和l=2的轨道角动量连续变量量子导引、量子纠缠、量子失谐和量子相干的退相干特性与高斯模式光场（l=0）的退相干特性相同，证明了利用轨道角动量复用连续变量量子资源提高量子通信容量的可行性；理论证明了利用原子系综相敏放大器可以提高连续变量纠缠态抵抗退相干的能力，能够延长连续变量纠缠态的传输距离。研究结果进一步推动了远距离、高容量量子信息网络的发展。