Optimization of Information Reconciliation for Decoy-State Quantum Key Distribution over a Satellite Downlink Channel

TL;DR

This paper enhances the efficiency of the information reconciliation step in satellite-based quantum key distribution, leading to longer secure keys by modeling and optimizing for time-varying channel conditions during satellite passes.

Contribution

It introduces an accurate model of satellite downlink signals and QBER, and optimizes IR using a-priori QBER information to improve key length in Decoy-State BB84 QKD.

Findings

Secure key length increased by nearly 3% in realistic scenarios.

Model accounts for link geometry, scintillation, and signal intensity variations.

Optimization improves IR efficiency during short satellite passes.

Abstract

Quantum key distribution (QKD) is a cryptographic solution that leverages the properties of quantum mechanics to be resistant and secure even against an attacker with unlimited computational power. Satellite-based links are important in QKD because they can reach distances that the best fiber systems cannot. However, links between satellites in low Earth orbit (LEO) and ground stations have a duration of only a few minutes, resulting in the generation of a small amount of secure keys. In this context, we investigate the optimization of the information reconciliation step of the QKD post-processing in order to generate as much secure key as possible. As a first step, we build an accurate model of the downlink signal and quantum bit error rate (QBER) during a complete satellite pass, which are time-varying due to three effects: (i) the varying link geometry over time, (ii) the scintillation effect, and (iii) the different signal intensities adopted in the Decoy-State protocol. Leveraging the a-priori information on the instantaneous QBER, we improve the efficiency of information reconciliation (IR) (i.e., the error correction phase) in the Decoy-State BB84 protocol, resulting in a secure key that is almost 3\% longer for realistic scenarios.