Optimal design and performance evaluation of free-space Quantum Key Distribution systems

TL;DR

This paper develops a comprehensive model for free-space ground-to-ground quantum key distribution systems, accounting for atmospheric effects, system design constraints, and finite-key analysis to optimize performance under daylight conditions.

Contribution

It introduces a detailed performance model that integrates atmospheric turbulence, system parameters, and finite-key effects for optimizing free-space QKD system design.

Findings

Channel fluctuation statistics are crucial for accurate secret key rate estimation.

Adaptive correction and filtering strategies improve daylight operation performance.

Optimal design choices depend on atmospheric conditions and system constraints.

Abstract

Free-space ground-to-ground links will be an integral part of future quantum communication networks. The implementation of free-space and fiber links in daylight inter-modal configurations are however still hard to achieve, due to the impact of atmospheric turbulence, which strongly decreases the coupling efficiency into the fiber. In this work, we present a comprehensive model of the performance of a free-space ground-to-ground quantum key distribution (QKD) system based on the efficient-BB84 protocol with active decoy states. Our model takes into account the atmospheric channel contribution, the transmitter and receiver telescope design constraints, the parameters of the quantum source and detectors, and the finite-key analysis to produce a set of requirements and optimal design choices for a QKD system operating under specific channel conditions. The channel attenuation is calculated considering all effects deriving from the atmospheric propagation (absorption, beam broadening, beam wandering, scintillation, and wavefront distortions), as well as the effect of fiber-coupling in the presence of a partial adaptive correction with finite control bandwidth. We find that the channel fluctuation statistics must be considered to correctly estimate the effect of the saturation rate of the single-photon detectors, which may otherwise lead to an overestimation of the secret key rate. We further present strategies to minimize the impact of diffuse atmospheric background in daylight operation by means of spectral and temporal filtering.