Practical source monitoring for continuous-variable quantum key distribution

Source monitoring is a matter of vital importance for continuous-variable quantum key distribution (QKD), since it is the first barrier to ensure the practical security. In a practical scenario, the difficulty arises with the existence of the laser intensity fluctuation, which not only contributes to the source noise but also causes the deviation of source monitoring result. We first illustrate the effect of the relative intensity noise (RIN) on the ultimate security by explicitly showing the parameter estimation procedure, and find that the secret key rate is overestimated in this situation. To defend the continuous-variable QKD system against potential attacks utilizing this impairment to conceal itself, a source monitoring scheme is devised by adopting the seminal one-time shot-noise unit calibration approach into the monitor module. It is shown that by using the practical source monitoring scheme the impact of the RIN can be modeled and monitored in real time to circumvent an overestimated secret key rate. This scheme also lowers the system complexity thus is suitable for widespread application.