Atmospheric effects on continuous-variable quantum key distribution

TL;DR

This paper analyzes how atmospheric turbulence and channel effects impact the performance of continuous-variable quantum key distribution, providing new formulas for fading channels and practical insights for real-world implementation.

Contribution

It introduces new key rate formulas for atmospheric fading channels in CVQKD, accounting for detection imperfections and turbulence effects, aiding experimental feasibility assessments.

Findings

Transmittance fluctuations mainly cause performance deterioration in horizontal links.

Pulse broadening under weak turbulence has negligible impact on transmittance.

Phase excess noise from arrival time fluctuations needs new compensation techniques.

Abstract

Compared to fiber continuous-variable quantum key distribution (CVQKD), atmospheric link offers the possibility of a broader geographical coverage and more flexible transmission.However, there are many negative features of the atmospheric channel that will reduce the achievable secret key rate, such as beam extinction and a variety of turbulence effects. Here we show how these factors affect performance of CVQKD, by considering our newly derived key rate formulas for fading channels,which involves detection imperfections, thus form a transmission model for CVQKD. This model can help evaluate the feasibility of experiment scheme in practical applications.We found that performance deterioration of horizontal link within the boundary layer is primarily caused by transmittance fluctuations (including beam wandering, broadening, deformation, and scintillation),while transmittance change due to pulse broadening under weak turbulence is negligible. Besides,we also found that communication interruptions can also cause a perceptible key rate reduction when the transmission distance is longer, while phase excess noise due to arrival time fluctuations requires new compensation techniques to reduce it to a negligible level. Furthermore, it is found that performing homodyne detection enables longer transmission distances, whereas heterodyne allows higher achievable key rate over short distances.