High-performance long-distance discrete-modulation continuous-variable quantum key distribution

We experimentally demonstrate a high-rate discretely modulated continuous-variable quantum key distribution over 80-km standard single-mode fiber with 2.5 GBaud, 16-symbol, two-ring constellation. With the help of well-designed digital signal processing algorithms, the excess noise of the system can be effectively suppressed. The achieved secret key rates are 49.02 Mbps, 11.86 Mbps, and 2.11 Mbps over 25-km, 50-km, and 80-km optical fiber, respectively, which achieve 67.4%, 70.0%, 66.5% of the secret key rate performance of a Gaussian-modulated protocol. Our work shows that it is feasible to build a high performance, long distance continuous variable quantum key distribution system with only a small constellation size.