Continuous-variable quantum key distribution (CVQKD) offers potential advantages of high secret key rate, making it suitable for high-speed metropolitan network applications. However, current CVQKD systems achieve only a few Mbps over typical transmission distances. This paper addresses fundamental experimental challenges and demonstrates a single-carrier four-state CVQKD achieving sub-Gbps key rates within a metropolitan area. Using a local local oscillator, ultra-low excess noise is achieved, and a high-efficiency post-processing setup is designed for secure key extraction. Secret key rates of 190.54 Mbps, 137.76 Mbps, and 52.48 Mbps (using linear channel assuming security analysis) and 233.87 Mbps, 133.6 Mbps, and 21.53 Mbps (using semidefinite programming security analysis) are achieved over 5 km, 10 km, and 25 km, respectively. This work paves the way for high-rate, large-scale CVQKD deployment in secure broadband networks.

Heng Wang, Yang Li, Yaodi Pi, Yan Pan, Yun Shao, Li Ma, Yichen Zhang, Jie Yang, Tao Zhang, Wei Huang, Bingjie Xu