Correction of beam wander for a free-space quantum key distribution system operating in urban environment

TL;DR

This paper introduces a high-speed automatic tracking system to correct beam wander in urban free-space quantum key distribution, enhancing performance by reducing turbulence effects and background noise.

Contribution

The paper presents a novel high-speed beam wander correction system with two design approaches for urban quantum communication environments.

Findings

Beam wander correction improves quantum bit error rate.

System enhances secret key rate in urban conditions.

Experimental results show potential for real-world deployment.

Abstract

Free-space quantum key distribution links in urban environment have demanding operating needs, such as functioning in daylight and under atmospheric turbulence, which can dramatically impact their performance. Both effects are usually mitigated with a careful design of the field of view of the receiver. However, a trade-off is often required, since a narrow field of view improves background noise rejection but it is linked to an increase in turbulence-related losses. In this paper, we present a high-speed automatic tracking system to overcome these limitations. Both a reduction in the field-of-view to decrease the background noise and the mitigation of the losses caused by atmospheric turbulence are addressed. Two different designs are presented and discussed, along with technical considerations for the experimental implementation. Finally, preliminary experimental results of beam wander correction are used to estimate the potential improvement of both the quantum bit error rate and secret key rate of a free space quantum key distribution system.