CV Quantum Communications with Angular Rejection Filtering: Modeling and Security Analysis

TL;DR

This paper models and analyzes the security of CV quantum key distribution over free-space links using angular rejection filtering to mitigate turbulence and misalignment effects, enhancing secure communication.

Contribution

It introduces an angular rejection filter model for CV-QKD, analyzing its impact on security and performance through simulations and parameter optimization.

Findings

Safe zone filtering reduces information leakage.

Proper parameter tuning maximizes secret key rate.

Larger apertures improve security but increase size.

Abstract

Continuous-variable quantum key distribution (CVQKD) over free-space optical links is a promising approach for secure communication, but its performance is limited by turbulence, pointing errors, and angular leakage that can be exploited by an eavesdropper. To mitigate this, we consider an angular rejection filter that defines a safe-zone at the receiver and blocks signals from outside the desired cone. A system and channel model is developed including turbulence, misalignment, and safe-zone effects, and information theoretic metrics are derived to evaluate security. Simulation results show that the safe zone significantly reduces information leakage and that careful tuning of beam waist, angular threshold, and aperture size is essential for maximizing the secret key rate. Larger apertures improve performance but increase receiver size, while longer links require sub 100 urad alignment accuracy. These results highlight safe-zone enforcement and parameter optimization as effective strategies for practical and secure CV-QKD.