CV MDI-QKD with noisy coherent states

Abstract

Continuous variable measurement-device-independent quantum key distribution (CV MDI-QKD) where legitimate communication parties, Alice and Bob, do not connect to each other directly but to an untrusted relay where the detection is performed can defend attacks that aim at measurement devices. It was recently shown that the preparation noise, although being trusted, was breaking the security of CV QKD. Hence, we study the security of continuous variable measurement-device-independent quantum key distribution based on noisy modulation of coherent states and investigate how the preparation noise influences the maximum transmission distance of the system. We propose a scheme of using a variable attenuator to attenuate decoder’s (Bob’s) mode to purify the coherent states he sends out under two-mode coherent attack. The simulation results show that when taking preparation noise into consideration the maximum transmission distance decreases seriously and our scheme can effectively compensate the detrimental effect of the preparation noise and improve the maximum transmission distance.