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Laser & Optoelectronics Progress

星地链路中光放大器对量子密钥分发的性能分析与改进

姜欢窈 Jiang Huanyao, 聂敏 Nie Min, 杨光 Yang Guang, 姚骏海 Yao Junhai

Published Jan 1, 2025• 1 citation

Abstract

研究了光放大器在星地链路中对离散调制连续变量量子密钥分发（DM-CV-QKD）系统的量子密钥率提升及其对系统安全性的影响。通过仿真分析发现，光放大器能够显著提高短距离通信中的量子密钥率，尽管四进制量子密钥分发和八进制量子密钥分发协议在此情境下有效提高了密钥率，但存在较大的退化区域，未能覆盖卫星到地面之间的安全通信距离，导致安全通信距离较短。为突破这一限制，提出了一种新型的十六进制双环调制方式，有效地减小了退化区域并增强了系统的整体可靠性，从而显著提升了密钥率并延长了安全通信距离。此外，还分析了湍流强度、光波长和水平仰角等因素对此系统性能的影响，结果表明，在强湍流条件下，使用高斯调制和十六进制双环调制方式，光放大器仍能有效提升信号质量，其增强区域可以覆盖近地轨道卫星的工作范围，证明了其在复杂环境中的应用价值与重要性。

DOI: 10.3788/lop242319

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研究了光放大器在星地链路中对离散调制连续变量量子密钥分发（DM-CV-QKD）系统的量子密钥率提升及其对系统安全性的影响。通过仿真分析发现，光放大器能够显著提高短距离通信中的量子密钥率，尽管四进制量子密钥分发和八进制量子密钥分发协议在此情境下有效提高了密钥率，但存在较大的退化区域，未能覆盖卫星到地面之间的安全通信距离，导致安全通信距离较短。为突破这一限制，提出了一种新型的十六进制双环调制方式，有效地减小了退化区域并增强了系统的整体可靠性，从而显著提升了密钥率并延长了安全通信距离。此外，还分析了湍流强度、光波长和水平仰角等因素对此系统性能的影响，结果表明，在强湍流条件下，使用高斯调制和十六进制双环调制方式，光放大器仍能有效提升信号质量，其增强区域可以覆盖近地轨道卫星的工作范围，证明了其在复杂环境中的应用价值与重要性。

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连续变量量子密钥分发（CV-QKD）协议在光纤信道中已经展现出可获得更高安全码率的能力。但是，CV-QKD协议可容忍的信道衰减相对较低，大气衰减、衍射、湍流等实际因素都会影响空间信道CV-QKD协议的可行性。低轨卫星与地面站接入时间相对较短，放大了有限密钥长效应对协议参数估计的影响。本研究分析了星地下行退化信道下的高斯调制CV-QKD协议，探讨了制备方差和协商效率对系统密钥生成的影响，结果显示，对于空间CV-QKD，无论协商效率是否完美，制备方差对密钥生成率的影响都不是单调的，存在一个最优值。本研究还探索了有限密钥长效应下用于参数估计的符号数量和符号传输率对密钥生成的影响（两者会显著影响系统的密钥生成），并针对不同的符号传输率，对用于参数估计的符号数量进行了优化。仿真结果可为空间信道高斯调制CV-QKD实验的设计和优化提供参考。

Continuous-variable quantum key distribution (CV-QKD) with a real local oscillator (LO) experiences a phase attack security challenge due to the reference pulses transmitted along with quantum signals over an unsecure quantum channel. In this paper, a phase attack on reference pulses of CV-QKD with a real LO is investigated. The performance of the discrete-modulated (DM) CV-QKD under this attack is analyzed analytically and by simulation, and compared with the Gaussian-modulated (GM) CV-QKD. It is found that such an attack by an eavesdropper's, significantly reduce the transmission distance for the GM based CV-QKD, whereas, the DM based CV-QKD shows a high tolerance to high phase noise. Based on phase attack monitoring, a new adaptive modulation scheme is proposed for CV-QKD to adaptively switch between GM and DM so as to maintain the optimum secret key rate.

The discrete-modulated continuous-variable quantum key distribution (DM-CV-QKD) could break the distance limitation of Gaussian-modulated CV-QKD. In practice, the high-performance error correction code plays an important role in DM-CV-QKD and affects the secure transmission distance. However, DM-CV-QKD usually works under low signal-to-noise ratio (SNR) and the design of high-performance error correction code under this condition is difficult, so that it would impose a limitation on further improvement of the secure distance. We propose a DM-CV-QKD with the machine-learning-based detector to further improve the secure distance. The numerical result shows that the proposed scheme could validly improve the system performance. Viewed from another perspective, the proposed scheme could be employed to overcome various impairments induced by the channel and thereby lower the demand of error correction codes on the SNR threshold of the quantum channel without compromising the system performance. The proposed scheme opens the door to applying machine leaning to directly process the raw secret key and improve the performance for CV-QKD systems.