Quantum key distribution (QKD) uses individual light quanta in quantum superposition states to guarantee unconditional communication security between distant parties. In practice, the achievable distance for QKD has been limited to a few hundred kilometers, due to the channel loss of fibers or terrestrial free space that exponentially reduced the photon rate. Satellite-based QKD promises to establish a global-scale quantum network by exploiting the negligible photon loss and decoherence in the empty out space. Here, we develop and launch a low-Earth-orbit satellite to implement decoy-state QKD with over kHz key rate from the satellite to ground over a distance up to 1200 km, which is up to 20 orders of magnitudes more efficient than that expected using an optical fiber (with 0.2 dB/km loss) of the same length. The establishment of a reliable and efficient space-to-ground link for faithful quantum state transmission constitutes a key milestone for global-scale quantum networks.
@article{arxiv.1707.00542,
title = {Satellite-to-ground quantum key distribution},
author = {Sheng-Kai Liao and Wen-Qi Cai and Wei-Yue Liu and Liang Zhang and Yang Li and Ji-Gang Ren and Juan Yin and Qi Shen and Yuan Cao and Zheng-Ping Li and Feng-Zhi Li and Xia-Wei Chen and Li-Hua Sun and Jian-Jun Jia and Jin-Cai Wu and Xiao-Jun Jiang and Jian-Feng Wang and Yong-Mei Huang and Qiang Wang and Yi-Lin Zhou and Lei Deng and Tao Xi and Lu Ma and Tai Hu and Qiang Zhang and Yu-Ao Chen and Nai-Le Liu and Xiang-Bin Wang and Zhen-Cai Zhu and Chao-Yang Lu and Rong Shu and Cheng-Zhi Peng and Jian-Yu Wang and Jian-Wei Pan},
journal= {arXiv preprint arXiv:1707.00542},
year = {2017}
}