Department of Modern Physics and Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, China.
Chinese Academy of Sciences (CAS) Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China.
Nature. 2017 Sep 7;549(7670):43-47. doi: 10.1038/nature23655. Epub 2017 Aug 9.
Quantum key distribution (QKD) uses individual light quanta in quantum superposition states to guarantee unconditional communication security between distant parties. However, the distance over which QKD is achievable has been limited to a few hundred kilometres, owing to the channel loss that occurs when using optical fibres or terrestrial free space that exponentially reduces the photon transmission rate. Satellite-based QKD has the potential to help to establish a global-scale quantum network, owing to the negligible photon loss and decoherence experienced in empty space. Here we report the development and launch of a low-Earth-orbit satellite for implementing decoy-state QKD-a form of QKD that uses weak coherent pulses at high channel loss and is secure because photon-number-splitting eavesdropping can be detected. We achieve a kilohertz key rate from the satellite to the ground over a distance of up to 1,200 kilometres. This key rate is around 20 orders of magnitudes greater than that expected using an optical fibre of the same length. The establishment of a reliable and efficient space-to-ground link for quantum-state transmission paves the way to global-scale quantum networks.
量子密钥分发（QKD）使用处于量子叠加态的单个光量子来保证远距离双方之间无条件的通信安全。然而，由于光纤或地面自由空间中存在的信道损耗会使光子传输速率呈指数级下降，因此 QKD 的可行距离限制在几百公里以内。基于卫星的 QKD 具有帮助建立全球规模的量子网络的潜力，因为在空旷的太空中几乎不会发生光子损耗和退相干。在这里，我们报告了一种低地球轨道卫星的开发和发射，用于实现诱骗态 QKD——一种在高信道损耗下使用弱相干脉冲的 QKD 形式，由于可以检测到光子数分裂窃听，因此是安全的。我们在长达 1200 公里的距离上实现了从卫星到地面的千赫兹密钥率。与使用相同长度光纤相比，这个密钥率大约高出 20 个数量级。可靠和高效的天地量子态传输链路的建立为全球规模的量子网络铺平了道路。
