中山大学孙仕海团队近日研究了基于机器学习增强量子比特同步的独立于参考帧的量子密钥分发。该研究于2025年5月19日发表于《中国科学：物理学 力学 天文学》杂志上。

即使在量子信息时代，量子密钥分发（QKD）也能实现理论上安全的信息通信。在所有QKD系统中，两个远程用户（通常称为Alice和Bob）之间的时钟同步是一个基本要求。这通常是通过从Alice向Bob发送额外的参考时钟信号来实现的。在这种方案中，需要额外的同步设备，增加了系统复杂性并引入了外部噪声。为了解决这些问题，研究组提出了一种新的同步技术，称为基于量子比特的同步方法。该方法使用量子信号直接同步两个用户，从而大大降低了系统复杂性。然而，之前基于量子比特的同步方法不适用于时间仓相位编码的量子密钥分配系统，因为多个时间滑块会对时间恢复产生干扰。 

研究组提出了一种基于机器学习增强量子比特的同步方法。通过引入K近邻模型，该方法可以有效地对时域相位编码QKD中的每个时间滑动进行分类，从而实现成功的时间恢复。他们使用独立于参考帧的时域相位编码（RFI）-QKD演示了该方法，并成功地在长达200公里的光纤卷轴上分发了安全密钥位。该工作简化了QKD系统的复杂性，显著推进了QKD的实际应用。

附：英文原文

Title: Reference-frame-independent quantum key distribution based on machine-learning-enhanced qubit-based synchronization

Author: Tian, Zhiyu, Xie, Ziran, Chen, Ye, Fan, Xiaodong, Huang, Jinquan, Mu, Tonglin, Guo, Junran, Wei, Kejin, Sun, Shihai

Issue&Volume: 2025-05-19

Abstract: Quantum key distribution (QKD) enables information-theoretically secure communication, even in the era of quantum information. In all QKD systems, clock synchronization between two remote users—commonly referred to as Alice and Bob—is a fundamental requirement. This is typically achieved by transmitting an additional reference clock signal from Alice to Bob. In such a scheme, additional synchronization devices are required, increasing system complexity and introducing external noise. To address these issues, a novel synchronization technology, called the qubit-based synchronization method, was proposed. This method directly synchronizes two users using quantum signals, thereby dramatically reducing system complexity. However, previous qubit-based synchronization methods are not applicable to time-bin phase-encoding QKD systems, as multiple time slides introduce disturbances to time recovery. In this paper, we propose a machine-learning-enhanced qubit-based synchronization method. By introducing a K-nearest neighbor model, this method can efficiently classify each time slide in time-bin phase-encoding QKD, thereby enabling successful time recovery. We demonstrate our method using a time-bin phase-encoding reference-frame-independent (RFI)-QKD and successfully distribute secure key bits over up to 200 km of fiber spools. Our work simplifies the complexity of QKD system and significantly advances the practical application of QKD.

DOI: 10.1007/s11433-024-2618-y

Source: https://link.springer.com/article/10.1007/s11433-024-2618-y