Free-space quantum key distribution during daylight and at night
Wenqi Cai, Yang Li, Bo Li, Ji-Gang Ren, Sheng‐Kai Liao, Yuan Cao, Liang Zhang, Yang Meng, Jincai Wu, Yu-Huai Li, Wei-Yue Liu, Juan Yin, Chao-Ze Wang, Wenbin Luo, Biao Jin, Chao-Lin Lv, Hao Li, Lixing You, Rong Shu, Ge-Sheng Pan, Qiang Zhang, Nai-Le Liu, Xiang‐Bin Wang, Jianyu Wang, Cheng-Zhi Peng, Jian-Wei Pan
Abstract
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.