Continuous Variable Quantum Key Distribution Experiment System And Security Research

This paper studies safety problems of continuous-variable quantum key distribution system. Specifically, it researches the defects of links or modules affecting the realistic system security from the perspective of system secret key rate in the concrete.1. Studying the influence of channel over attenuation on the system secret key rate. When the channel is established, its transmission efficiency is fixed, but the channel transmittance is reduced if the channel is attenuated by Eve. We found that the channel transmittance’s reduction will lead to decrease of the secret key rate through theoretical and experimental research. The key could be stolen by Eve when the key rate is below zero.2. Studying the influence of non-ideal phase compensation on system secret key rate. Continuous-variable quantum key distribution system needs phase modulation, but the quantum signal is vulnerable and easily been affected by the environment, and then leads to phase deviation, this deviation will affect the security of the system. Through the research we found that phase deviation reaching to some extent also leads to the decline of secret key rate, eventually to below zero. This potential safety hazard has a high requirement on phase compensation module of system to ensure the system in a safe working condition.3. Studying the influence of the change of shot noise variance on system secret key rate. Shot noise variance is an important parameter in the system, and other parameters are all normalized with it. So the changes of shot noise variance will change other parameters. This parameter is supposed to be constant in the previous study. In fact, Eve can change local oscillator’s intensity to change shot noise variance completely. The theoretical analysis shows that Eve adopting Intercept-Resend Attack can steal the key by changing the shot noise variance under the condition of not reducing secret key rate. This is a serious security loophole, we can’t judge potential safety hazard through the secret key rate, so our research proposed real-time monitoring of shot noise variance to avoid this potential safety hazard.4. This paper not only presents the theoretical analysis, but also shows the experimental verification. First, we built a continuous-variable quantum key distribution system which is based on the analysis of real-time key rate. It can distribute the key, extract parameters of the real-time system at the same time, exchange the data and evaluate secret key rate for monitoring the realistic system security and finding potential safety hazard to warn us in time. We had carried out the verification experiments based on the system. First of all, we had verified the influence of channel attenuation on secret key rate. When channel is attenuated by the attenuator, the system’s key rate declined. Second, when the phase compensation module is provided with additional value of phase compensation, we had verified the influence of phase compensation on secret key rate after the introduction of phase interference. Finally, we proposed shot noise variance calibration technology in order to detect shot noise variance in real-time which is showed by linear relationship between the local oscillator intensity and the shot noise variance. We have reached the conclusion which is the influence of shot noise variance on the system secret key rate through the experiment.