AI 中文总结
该研究在620米自由空间+2公里光纤的混合信道上实现了压缩态与相干态CV-QKD，通过统一自适应后处理框架恢复19%额外密钥，为异构量子网络提供了新途径。
AI 中文摘要
量子网络将结合光纤与自由空间链路，但连续变量量子密钥分发（CV-QKD）的开发主要针对单一介质，而在级联光纤-自由空间信道上的操作仍未被充分探索。两种介质提出了截然不同的要求：光纤传输稳定且允许较长的处理间隔，而大气传播会引入透射率波动，降低安全性，必须在短时间尺度上解决。本文中，我们演示了一种本地生成本振的CV-QKD，同时采用高斯调制的相干态与压缩态，在包含620米自由空间链路和2公里已部署光纤的混合信道上实现，总损耗高达20分贝。我们没有为每种介质调整光学系统，而是将信道适配转移到后处理环节，通过统一的自适应后处理框架，该框架耦合了基于透射率的聚类、通过协方差矩阵平均或去衰落实现的残余衰落缓解，以及速率自适应的盲协调，仅这一环节就额外恢复了高达19%的密钥。同样的自适应处理原理被应用于两种协议，同时考虑它们不同的安全性分析和统计要求，在各自信道条件下，相干态协议的渐近密钥率为0.42兆比特每秒，压缩态协议的渐近密钥率为0.93兆比特每秒，从而在已部署的大气信道上实现了压缩态CV-QKD。这些结果表明，对传输介质的适配可在很大程度上转移到数据处理层，为跨越光纤、地面自由空间和卫星链路的异构量子网络提供了一条途径。
英文摘要
Quantum networks will combine optical fibre with free-space links, yet continuous-variable quantum key distribution (CV-QKD) has been developed predominantly for one medium or the other, while operation across concatenated fibre-free-space channels remains largely unexplored. The two media impose contrasting requirements: fibre transmission is stable and permits long processing intervals, whereas atmospheric propagation imposes transmittance fluctuations that degrade security and must be resolved on short timescales. Here we demonstrate a locally generated local oscillator CV-QKD with both Gaussian-modulated coherent and squeezed states over a deployed hybrid channel comprising a 620-m free-space link and 2 km of deployed fibre, with a total loss up to 20 dB. Rather than adapting the optics to each medium, we move channel adaptation to the post-processing, through a unified adaptive post-processing framework coupling transmittance-based clustering, residual-fading mitigation by covariance-matrix averaging or de-fading, and rate-adaptive blind reconciliation, which alone recovers up to 19% additional key. The same adaptive-processing principle is applied to both protocols, while accounting for their different security analyses and statistical requirements, yielding asymptotic secret-key rates of 0.42 Mbit per sec for the coherent-state protocol and 0.93 Mbit per sec for the squeezed-state protocol under the respective channel conditions, and establishing squeezed-state CV-QKD over a deployed atmospheric channel. These results show that adaptation to the transmission medium can largely be transferred to the data-processing layer, providing a route towards heterogeneous quantum networks spanning fibre, terrestrial free-space and satellite links.
