Implementation of quantum key distribution surpassing the linear rate-transmittance bound

• Published in: Nature photonics Vol. 14; no. 7; pp. 422 - 425
• Main Authors: Fang, Xiao-Tian, Zeng, Pei, Liu, Hui, Zou, Mi, Wu, Weijie, Tang, Yan-Lin, Sheng, Ying-Jie, Xiang, Yao, Zhang, Weijun, Li, Hao, Wang, Zhen, You, Lixing, Li, Ming-Jun, Chen, Hao, Chen, Yu-Ao, Zhang, Qiang, Peng, Cheng-Zhi, Ma, Xiongfeng, Chen, Teng-Yun, Pan, Jian-Wei
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2020; Nature Publishing Group
• Subjects: 639/624/400/482; 639/766/483/481; Applied and Technical Physics; Compensation; Injection; Lasers; Letter; Linear functions; Phase matching; Physics; Physics and Astronomy; Quantum cryptography; Quantum Physics; Transmittance
• ISSN: 1749-4885; 1749-4893
• DOI: 10.1038/s41566-020-0599-8

Quantum key distribution (QKD) 1 , 2 offers a long-term solution to secure key exchange. Due to photon loss in transmission, it was believed that the repeaterless key rate is bounded by a linear function of the transmittance, O ( η ) (refs. 3 , 4 ), limiting the maximal secure transmission distance 5 , 6 . Recently, a novel type of QKD scheme has been shown to beat the linear bound and achieve a key rate performance of O ( η ) (refs. 7 – 9 ). Here, by employing the laser injection technique and the phase post-compensation method, we match the modes of two independent lasers and overcome the phase fluctuation. As a result, the key rate surpasses the linear bound via 302 km and 402 km commercial-fibre channels, over four orders of magnitude higher than existing results 5 . Furthermore, our system yields a secret key rate of 0.118 bps with a 502 km ultralow-loss fibre. This new type of QKD pushes forward long-distance quantum communication for the future quantum internet. Phase-matching quantum key distribution is implemented with a 502 km ultralow-loss optical fibre. The fluctuations of the laser initial phases and frequencies are suppressed by the laser injection technique and the phase post-compensation method.