303公里量子密钥分发实测，验证了商用系统在复杂光纤网络中的可行性。
Deployed trusted-node quantum key distribution over 300 km with a multi-core fiber access link
- 采用双段光纤：270公里单模光纤+33公里多芯光纤，模拟城域接入链路。
- 在303公里总距离上实现稳定密钥分发，支持共传以太网与噪声干扰。
- 展示实际应用中密钥速率波动对加密图像质量的影响，贴近真实场景。
量子密钥分发（QKD）正逐步迈向真实通信网络的部署，但长距离、异构光纤基础设施及与经典业务共存带来严峻挑战。本文演示了林雪平大学与瑞典国家量子通信基础设施斯德哥尔摩节点间，通过270公里已部署单模光纤和33公里多芯光纤（MCF）段（模拟城域接入链路）组成的303公里链路，实现可信节点QKD。两段链路均使用商用QKD系统，接收端外接超导纳米线单光子探测器，可在标准内部门控探测器无法支持的损耗条件下运行。系统在动态切换MCF芯道的同时，支持共传以太网流量及向其他芯注入宽带光噪声。结果表明，商用QKD可集成至高要求、可重构的光纤基础设施中，适用于未来混合量子-经典网络。最后，利用生成的密钥进行一次性密码本加密图像传输，结果显示图像保真度显著依赖可用密钥量及压缩算法选择，揭示了实际应用中基于QKD加密的关键挑战。
原文摘要 · Abstract (English)
Quantum key distribution (QKD) is increasingly considered for deployment in realistic communication networks, where long distances, heterogeneous fiber infrastructure, and coexistence with classical traffic present substantial challenges. Here, we demonstrate trusted-node QKD between Linköping University and the Stockholm hub of the Swedish national quantum communication infrastructure over 270 km of deployed single-mode fiber, extended by a 33 km multi-core fiber (MCF) segment emulating a metropolitan access link, for a total distance of 303 km. The two sub-links use commercial QKD systems whose receivers are interfaced with external superconducting nanowire single-photon detectors, enabling operation at losses beyond those supported by standard internal gated-mode detectors. We operate the link while actively switching the QKD channel between two MCF cores, with co-propagating Ethernet traffic and injected broadband optical noise in the other cores. The results demonstrate the integration of commercial QKD into demanding, dynamically reconfigurable fiber infrastructure relevant to future hybrid quantum-classical networks. Finally, using the generated secret keys, we illustrate how limited and time-varying QKD throughput affects one-time-pad-protected image transmission: image fidelity depends strongly on the available QKD-generated key budget and the choice of compression algorithm, highlighting application-level challenges for QKD-based encryption in realistic scenarios.
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