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Zhongguo kexue. Wulixue Lixue Tianwenxue

Advances in practical long-distance quantum key distribution

Hai Xu, Cong Jiang, Xiaolong Hu, Zongwen Yu, XiangBin WANG

Published Jul 7, 2026• 0 citations
Publisher

Abstract

本文综述远距离实用化量子密钥分发(Quantum Key Distribution, QKD)的历史、现状和进展, 重点梳理诱骗态、测量设备无关(Measurement-Device-Independent, MDI) QKD、双场(Twin-Field, TF) QKD、“发送/不发送”(Sending-or-Not-Sending, SNS)协议与侧信道安全(Side-Channel-Secure, SCS)协议等技术路线的理论进展及其在远距离实用化 QKD 实验和工程中的应用. 诱骗态方法解决了弱相干光源多光子成分带来的安全问题,而MDI-QKD则从协议层面彻底免疫了探测端的所有侧信道攻击. 针对信道损耗导致的远距离成码瓶颈, TF-QKD和SNS协议利用中间节点单光子干涉机制使密钥率呈信道透射率的平方根标度,从而突破无中继线性界.特别地, SNS协议凭借其对相位校准误差的高容忍度, 已成功应用于千公里级光纤QKD重大实验突破、现场商用户外光纤及片上集成QKD网络等多个关键应用场景. 以SNS协议为代表的双场QKD技术框架,为推动远距离QKD从实验室研究转向实际应用提供了重要路径. SCS协议利用真空态无侧信道的特性与映射安全性框架,建立了源端全空间态的安全性,且保持测量设备无关安全性.

DOI
10.1360/sspma-2026-0370

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Sending-or-not sending twin-field quantum key distribution (SNS TF-QKD) has the advantage of tolerating large amounts of misalignment errors, and its key rate can exceed the linear bound of repeaterless quantum key distribution. However, the weak randomness in a practical QKD system may lower the secret key rate and limit its achievable communication distance, thus compromising its performance. In this paper, we analyze the effects of the weak randomness on the SNS TF-QKD. The numerical simulation shows that SNS TF-QKD can still have an excellent performance under the weak random condition: the secret key rate can exceed the PLOB boundary and achieve long transmission distances. Furthermore, our simulation results also show that SNS TF-QKD is more robust to the weak randomness loopholes than the BB84 protocol and the measurement-device-independent QKD (MDI-QKD). Our results emphasize that keeping the randomness of the states is significant to the protection of state preparation devices.
The twin-field quantum key distribution (TF-QKD) and its variants can overcome the fundamental rate-distance limit of QKD. However, their physical implementations with the side channels remain the subject of further research. We test the side channel of a type of external intensity modulation that applies a Mach–Zehnder-type electro-optical intensity modulator, which shows the distinguishability of the signal and decoy states in the frequency domain. Based on this security loophole, we propose a side-channel attack, named the passive frequency-shift attack, on the imperfect implementation of the sending or not-sending (SNS) TF-QKD protocol. We analyze the performance of the SNS protocol with the actively odd-parity pairing (AOPP) method under the side-channel attack by giving the formula of the upper bound of the real secret key rate and comparing it with the lower bound of the secret key rate under Alice and Bob’s estimation. The simulation results quantitatively show the effectiveness of the attack on the imperfect devices at a long distance. Our results emphasize the importance of practical security at the light source and might provide a valuable reference for device selection in the practical implementation of the SNS protocol.
本研究探讨了自发参量下转换（Spontaneous Parametric Down-Conversion，SPDC）光源的光谱特性对量子密钥分发（Quantum Key Distribution，QKD）系统性能的影响。通过引入光谱自由度，对光子数分布进行了更为准确的建模，揭示了实际SPDC光源的分布特性可能不同于传统的泊松或热分布。研究表明，不同光谱结构会导致安全密钥率的显著差异，错误的分布假设可能导致安全性问题。本文提出的模型可用于优化QKD系统的设计，提高量子通信的安全性和传输距离。
Quantum key distribution (QKD) could help to share a secure key between two distant peers. In recent years, twin-field (TF) QKD has been widely investigated because of its long transmission distance. One of the popular variants of TF QKD is sending-or-not-sending (SNS) QKD, which has been experimentally verified to realize 1000-km level fiber key distribution. In this article, we introduce phase postselection into the SNS protocol. With this modification, the probability of selecting ``sending'' can be substantially improved. The numerical simulation shows that the transmission distance can be improved both with and without the actively odd-parity pairing method. The case of discrete phase randomization is also analyzed, a similar improvement on distance can be seen.
基于量子存储辅助的测量设备无关量子密钥分发（MDI-QKD）协议原理上能有效提升量子密钥分发系统的传输距离和密钥率，但现有三强度诱骗态方案受有限长效应影响严重，仍存在密钥率低、安全传输距离受限等问题。针对以上问题，本文提出了一种基于双参数扫描的量子存储辅助MDI-QKD协议，一方面，通过使用四强度诱骗态方法降低有限长效应的影响；另一方面，结合集体约束模型与双参数扫描算法来优化有限样本下的单光子计数率和相位误码率的估算精度，从而有效提升系统的整体性能。同时，本文开展了相关数值仿真计算，仿真结果显示，本方案与现有其他同类MDI-QKD方案，比如基于存储辅助的三强度诱骗态方案以及不使用存储的四强度诱骗态方案相比，在相同的实验条件下，分别提升了超过30公里和100公里的安全传输距离。因此，本文工作将为未来发展远距离量子通信网络提供重要的参考价值。