Entanglement-based secure quantum cryptography over 1,120 kilometres

Juan Yin, Yu-Huai Li, Sheng-Kai Liao, Meng Yang, Yuan Cao, Liang Zhang, Ji-Gang Ren, Wen-Qi Cai, Wei-Yue Liu, Shuang-Lin Li, Rong Shu, Yong-Mei Huang, Lei Deng, Li Li, Qiang Zhang, Nai-Le Liu, Yu-Ao Chen, Chao-Yang Lu, Xiang-Bin Wang, Feihu Xu, Jian-Yu Wang, Cheng-Zhi Peng (), Artur K. Ekert and Jian-Wei Pan ()
Additional contact information
Juan Yin: University of Science and Technology of China
Yu-Huai Li: University of Science and Technology of China
Sheng-Kai Liao: University of Science and Technology of China
Meng Yang: University of Science and Technology of China
Yuan Cao: University of Science and Technology of China
Liang Zhang: University of Science and Technology of China
Ji-Gang Ren: University of Science and Technology of China
Wen-Qi Cai: University of Science and Technology of China
Wei-Yue Liu: University of Science and Technology of China
Shuang-Lin Li: University of Science and Technology of China
Rong Shu: University of Science and Technology of China
Yong-Mei Huang: Chinese Academy of Sciences
Lei Deng: Shanghai Engineering Center for Microsatellites
Li Li: University of Science and Technology of China
Qiang Zhang: University of Science and Technology of China
Nai-Le Liu: University of Science and Technology of China
Yu-Ao Chen: University of Science and Technology of China
Chao-Yang Lu: University of Science and Technology of China
Xiang-Bin Wang: University of Science and Technology of China
Feihu Xu: University of Science and Technology of China
Jian-Yu Wang: University of Science and Technology of China
Cheng-Zhi Peng: University of Science and Technology of China
Artur K. Ekert: University of Oxford
Jian-Wei Pan: University of Science and Technology of China

Nature, 2020, vol. 582, issue 7813, 501-505

Abstract: Abstract Quantum key distribution (QKD)1–3 is a theoretically secure way of sharing secret keys between remote users. It has been demonstrated in a laboratory over a coiled optical fibre up to 404 kilometres long4–7. In the field, point-to-point QKD has been achieved from a satellite to a ground station up to 1,200 kilometres away8–10. However, real-world QKD-based cryptography targets physically separated users on the Earth, for which the maximum distance has been about 100 kilometres11,12. The use of trusted relays can extend these distances from across a typical metropolitan area13–16 to intercity17 and even intercontinental distances18. However, relays pose security risks, which can be avoided by using entanglement-based QKD, which has inherent source-independent security19,20. Long-distance entanglement distribution can be realized using quantum repeaters21, but the related technology is still immature for practical implementations22. The obvious alternative for extending the range of quantum communication without compromising its security is satellite-based QKD, but so far satellite-based entanglement distribution has not been efficient23 enough to support QKD. Here we demonstrate entanglement-based QKD between two ground stations separated by 1,120 kilometres at a finite secret-key rate of 0.12 bits per second, without the need for trusted relays. Entangled photon pairs were distributed via two bidirectional downlinks from the Micius satellite to two ground observatories in Delingha and Nanshan in China. The development of a high-efficiency telescope and follow-up optics crucially improved the link efficiency. The generated keys are secure for realistic devices, because our ground receivers were carefully designed to guarantee fair sampling and immunity to all known side channels24,25. Our method not only increases the secure distance on the ground tenfold but also increases the practical security of QKD to an unprecedented level.

Date: 2020
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DOI: 10.1038/s41586-020-2401-y

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