A Continuous-variable Quantum Repeater Protocol Enhanced with Multiplexing and Thermal Noise

The continuous-variable quantum repeater (CVQR) plays a crucial role in continuous-variable quantum key distribution (CV-QKD). It can largely extend the security distance limit of CV-QKD. Currently, the majority of CVQR designs relies on the use of noiseless linear amplifiers for entanglement distillation. However, practical noiseless linear amplifiers may reduce communication performances and suffer from low success rates due to the truncation noise produced during the amplification. To solve these problems, we propose an improved CVQR protocol assisted by mode-multiplexing and thermal noises. The results show the advantage of our protocol: at 100km, the success probability of our protocol is 0.4011 while that of the original protocol is 0.1177; the key rate under the collective attack is 1.3659 bits/pulse in our protocol while that of the original protocol is 0.1471 bits/pulse at 500 km. The CVQR protocol proposed in this work paves the way for long-distance CV-QKD.