Geng Chai

The post-processing process is an indispensable part of the continuous variable quantum key distribution (CVQKD), which converts partially relevant and partially secure measurement data to a completely consistent and information-theoretic secure key. Among them, parameter estimation is an important means of evaluating system parameters, and provides parameter basis for subsequent key extraction processes. However, the existed methods usually divide the free space into several relatively stable subchannels and use sampling estimation to achieve parameter estimation, which are limited by the quality and quantity of statistical samples. Here, we firstly propose a free-space parameter estimation scheme based on Bayesian estimation. Experiment has been proven that Bayesian schemes has advantages in estimation accuracy and stability compared to sampling statistical schemes, and has good performance in both free space and fiber channels, with high robustness and accuracy. Moreover, key reconciliation is also a highly anticipated aspect of CVQKD post-processing. But when the signal-to-noise ratio of the quantum channel changes, constant-bit-rate correction codes lead to a decrease in reconciliation efficiency, further deteriorating the system performance. We further propose a rate-adaptive Polar code reconciliation scheme and a scheme based on intermediate channel low-density parity check code cascaded polar code (IC-LDPC Polar code) to improve reconciliation efficiency and cope with practical long-distance CVQKD systems.

The signal of the photon must be phase modulated by Phase Modulation(PM), which plays a very important role in a continuous-variable quantum key distribution system. However, there may exits a drift of voltage in actual system. In this paper, we study the influence of the imperfect PM on the system performance of the CVQKD system. The result shows that the imperfect PM can threat the security of CVQKD system and choosing a reasonable noise module can be passively improved the security of system. We also propose a way to contain modulation noise in practical CVQKD systems.