Feasibility of continuous-variable quantum key distribution with noisy coherent states

TL;DR

This paper investigates the security of continuous-variable quantum key distribution using noisy coherent states, highlighting the impact of different trusted noises and proposing purification to mitigate preparation noise.

Contribution

It introduces a sender-side state purification method to counteract preparation noise, enhancing the robustness of quantum key distribution under realistic conditions.

Findings

Purification compensates for preparation noise in QKD.

Receiver-side detection noise does not compromise security.

Purification remains effective with realistic reconciliation constraints.

Abstract

We address security of the quantum key distribution scheme based on the noisy modulation of coherent states and investigate how it is robust against noise in the modulation regardless of the particular technical implementation. As the trusted preparation noise is shown to be security breaking even for purely lossy channels, we reveal the essential difference between two types of trusted noise, namely sender-side preparation noise and receiver-side detection noise, the latter being security preserving. We consider the method of sender-side state purification to compensate the preparation noise and show its applicability in the realistic conditions of channel loss, untrusted channel excess noise, and trusted detection noise. We show that purification makes the scheme robust to the preparation noise (i.e., even the arbitrary noisy coherent states can in principle be used for the purpose of quantum key distribution). We also take into account the effect of realistic reconciliation and show that the purification method is still efficient in this case up to a limited value of preparation noise.