We perform security analysis of a passive continuous-variable quantum key distribution (CV-QKD) protocol by considering the finite-size effect. In the passive CV-QKD scheme, Alice utilizes thermal sources to passively make preparation of quantum state without Gaussian modulations. With this technique, the quantum states can be prepared precisely to match the high transmission rate. Here, both asymptotic regime and finite-size regime are considered to make a comparison. In the finite-size scenario, we illustrate the passive CV-QKD protocol against collective attacks. Simulation results show that the performance of passive CV-QKD protocol in the finite-size case is more pessimistic than that achieved in the asymptotic case, which indicates that the finite-size effect has a great influence on the performance of the single-mode passive CV-QKD protocol. However, we can still obtain a reasonable performance in the finite-size regime by enhancing the average photon number of the thermal state.

量子密钥分发融合经典通信方案将连续变量量子密钥分发和经典通信合并到了一起, 为将来在现有的光网络上同时进行密钥分发和经典通信提供了一个有效的方法. 然而, 在量子信号上叠加一个经典信号将会给连续变量量子密钥分发系统引入过噪声从而大大降低了系统的性能. 本文提出基于光前置放大器的量子密钥分发融合经典通信方案, 即在接收端插入光前置放大器来提升系统的性能. 首先, 在相同比特误码率条件下, 光前置放大器对信号的放大能够降低对发送端经典信号调制振幅的要求, 从而降低经典信号对量子信号的噪声影响; 其次, 光前置放大器能够补偿接收端探测器的不完美; 再次, 对于本地本振光的情形, 放大器还能放大弱相位参考脉冲, 从而降低参考脉冲散粒噪声带来的相位过噪声. 在实际可达到的系统参数下, 数值仿真结果表明本文提出的方案相比于原方案在安全密钥率和传输距离上都能够有很好的提升. 这些结果表明本方案为量子密钥分发融合经典通信方案的进一步发展和实际应用提供了一个十分有效而实用的方法.