Current satellite-based quantum key distribution (QKD) is limited to nighttime operations, and the reliance on microwave communication for key distillation leads to significant delays, often spanning several days. These challenges collectively hinder the establishment of a practical global-scale quantum network. Here, by developing a 625-MHz inherently robust decoy-state light source and daytime noise suppression close to the Fourier transform limitation, we achieve QKD covering all the 24 h of the day over a 20-km terrestrial free-space channel, resulting in an average secure key rate of approximately 495 bps. Additionally, bidirectional laser communication is integrated into the QKD transmitter and the ground station to enable real-time key distillation, improving the timeliness from days to real time. This comprehensive verification lays a solid foundation and paves the way for all-day real-time QKD with quantum satellites.

中文翻译：

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白天和夜间的自由空间量子密钥分发


目前基于卫星的量子密钥分发（QKD）仅限于夜间操作，并且依赖微波通信进行密钥提取会导致严重的延迟，通常会持续数天。这些挑战共同阻碍了实用的全球规模量子网络的建立。在这里，通过开发 625 MHz 固有鲁棒的诱饵态光源和接近傅里叶变换极限的白天噪声抑制，我们实现了覆盖 20 公里地面自由空间信道全天 24 小时的 QKD，从而产生平均安全密钥速率约为 495 bps。此外，QKD发射机和地面站中集成了双向激光通信，可实现实时密钥蒸馏，将时效性从几天提高到实时。此次全面验证为量子卫星全天时实时量子密钥分发奠定了坚实的基础并铺平了道路。