Continuous-variable QKD network in Qingdao*

Continuous-variable quantum key distribution (QKD) is a very attractive method for the physical layer protection of information transmission by secure distribution of private keys, as it uses standard telecom components that operate at room temperature and it has higher secret key rates (bits per channel use) over metropolitan areas. The longest distance of continuous-variable QKD field tests has reached 50 km, which is enough to support the construction of metropolitan networks. Here, we report the long-term performance of three nodes continuous-variable QKD network in Qingdao, which is the first continuous-variable QKD application demonstration with clear application scenarios over a long period of time through existing commercial optical fiber links. The average secret key rate achieves higher than 12.00 kbps over 71.03 km optical fiber line. The system has been running for 28 days stably with a reliable performance, which paves the way to deploy continuous-variable QKD in metropolitan settings.