System design and realisation towards optimising secure key bits in free space QKD

TL;DR

This paper presents a practical framework for implementing and optimizing the BB84 quantum key distribution protocol, addressing real-world challenges and enhancing key generation rates through calibration, synchronization, and novel sampling techniques.

Contribution

It introduces a systematic, adaptable framework for QKD implementation, including algorithms and protocols that improve key rate and security reliability in practical settings.

Findings

Optimizing temporal window improves key rate and QBER.

Random sampling yields more reliable error estimation.

Integration of EPCD boosts key generation performance.

Abstract

Quantum Key Distribution (QKD) is rapidly transitioning from cutting-edge laboratory research to real-world deployment in established communication networks. Although QKD promises future-proof security, practical challenges stil exist due to imperfections in physical devices. Many protocols offer strong security guarantees, but their implementation can be complex and difficult. To bridge this gap, we present a practical and systematic framework for implementing QKD, focused on the BB84 protocol but designed with broader applicability in mind. The article includes key concepts for device calibration, synchronisation,optical alignment, and key post-processing. We outline a simple algorithm for key sifting that is easily implementable in hardware. Our results highlight the importance of selecting the temporal window to optimise both the key rate and the quantum bit error rate (QBER). In addition, we show that random sampling of the sifted key bits for error estimation yields more reliable results than sequential sampling. We also integrate the Entrapped Pulse Coincidence Detection (EPCD) protocol to boost key generation rates, further enhancing performance. Although our work focuses on BB84, the techniques and practices outlined are general enough to support a wide range of QKD protocols. This makes our framework a valuable tool for both research and real-world deployment of secure quantum communication systems.