7 km free-space time-bin quantum key distribution
Bo-Yang Qiu, Yang Li, Gao‐Qiang Wang, Li-Ying Han, H. Y. Fu, Yang Zhang, Nan Wu, Na Xiao, Zhi-Lin Xie, Ren-De Liu, Dongdong Li, Chao-Ze Wang, Wen-Qi Cai, Juan Yin, Ji-Gang Ren, Sheng‐Kai Liao, Cheng-Zhi Peng · Optics Express · 2025
Satellite-based quantum key distribution (QKD) holds the potential to establish global quantum communication networks. While satellite QKD has been demonstrated using polarization encoding, time-bin encoding offers distinct advantages, such as simplifying polarization-maintaining telescope designs and being insensitive to satellite-ground relative motion. In this work, we developed a 625-MHz QKD light source using a robust Sagnac-interferometer-based modulation scheme and subsequently demonstrated time-bin QKD over a 7 km urban terrestrial free-space channel. This experiment successfully operated over a channel traversing an equivalent atmospheric thickness and loss exceeding that of typical satellite-to-ground links, achieving a low quantum bit error rate of 0.87% and a secure key rate of 134 [email protected] dB. Furthermore, by using a half-wave plate to simulate the polarization-basis-rotation inherent in such links, we verified the robustness of time-bin encoding for satellite scenarios. The results validate time-bin encoding as a compelling alternative and lay the technical foundation for future satellite QKD applications.