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连续变量偏振纠缠态光场可以直接与原子系综相互作用，是构建量子网络的重要量子资源之一。然而，连续变量偏振纠缠在信道中的传输特性尚不清楚。本文针对连续变量两组份偏振纠缠在噪声信道中的传输特性进行了理论研究。通过将两组份正交分量纠缠光分别和强相干光耦合，得到连续变量两组份偏振纠缠态光场。将两组份偏振纠缠态光场分别经过两个相同损耗和相同噪声的信道传输，我们根据偏振纠缠的不可分判据，理论分析了传输后光场的偏振纠缠特性。结果显示，当损耗信道的传输效率不为0时，两组份偏振纠缠一直存在。而在噪声信道中传输时，随着额外噪声的增大，连续变量两组份偏振纠缠态光场的不可分程度逐渐降低。当额外噪声超过(η-ηe-2r)/(1-η)时，偏振纠缠态光场的不可分性消失。本文对基于连续变量偏振纠缠态的量子通信具有一定的参考价值。
Abstract：Objective. Continuous-variable polarization entangled state of light, which can directly interact with the atomic ensemble, is an important quantum resource for the construction of quantum network. Compared with the continuous-variable quadrature entangled state of light, the continuous-variable polarization entangled state of light is a bright beam and the detection of it is simpler than the continuous-variable quadrature entangled state of light because of the detection without the local oscillator. Toward the practical applications, the transmission of quantum states is a crucial stage for quantum communication. Although the transmission of continuous-variable polarization squeezed light has been achieved experimentally, the transmission characteristics of continuous-variable polarization-entangled states in the quantum channel remain unclear. Therefore, the research of the transmission characteristics of continuous-variable polarization entangled light in noisy channels is significant.Methods. In this letter, we present a theoretical study on the transmission characteristics of continuous-variable bipartite polarization entanglement in noisy channels. Continuous-variable bipartite polarization entangled state of light can be generated by coupling two quadrature entangled states and two strong coherent beams with orthogonal polarization on two polarization beam splitters. Then, through distributing these two polarization-entangled beams into two identical lossy channels and two identical noisy channels, respectively, to users, the users measure the variances of Stokes operators of their received light by combining halfwave plate, quarter-wave plate, polarization beam splitter and detector, and send the measured results to another side by classical communication. Finally, they can assess the degree of inseparability based on the criterion of continuous-variable polarization entanglement.Results and discussions. We find the degree of inseparability increases with the increase of squeezing parameter when there is no transmission. When the continuous-variable bipartite polarization entangled light is distributed in lossy channels, the results that the inseparability of polarization entangled light after transmission in lossy channels show that polarization entanglement of the two beams will always maintain. However, the degree of inseparability of polarization-entangled light decreases with the increased excess noise in noisy channels. When the excess noise extends the boundary of(η-ηe-2r)/(1-η), the polarization entanglement disappears which means the disappearance of the inseparability of polarization entanglement.Conclusions. We have theoretically analyzed the inseparability of polarization entangled state of light after transmission in noisy channels. The squeezing parameter, transmission efficiency and excess noise are key factors of the transmission characterization of continuous-variable polarization entanglement. Then we find a boundary about excess noise to maintain the inseparability of continuous-variable polarization entanglement when squeezing parameter and transmission efficiency are ensured. This letter provides a theoretical reference for quantum communication based on continuous-variable polarization-entangled states.
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基本信息:
中图分类号:O431.2
引用信息:
[1]刘瑞,任思宇,李雅琳,等.噪声信道连续变量偏振纠缠的传输特性[J].量子光学学报,2025,31(04):15-22.
基金信息:
国家自然科学基金项目（12434015;62275145）; 山西省基础研究计划项目（20210302121002;202403021224001）; 山西省“1331工程”重点学科建设项目（晋教科[2021]4号）