Practical round-robin differential-phase-shift quantum key distribution

TL;DR

This paper enhances a round-robin differential-phase-shift QKD protocol by applying tagging and decoy-state methods, demonstrating it can tolerate high error rates close to 50% under realistic conditions.

Contribution

It introduces a tight key rate bound and practical analysis for the protocol, improving its robustness and applicability in real-world quantum communication.

Findings

Protocol tolerates channel error rates close to 50%

Employs tagging and decoy-state techniques for security analysis

Practical conditions considered with background noise and misalignment

Abstract

The security of quantum key distribution (QKD) relies on the Heisenberg uncertainty principle, with which legitimate users are able to estimate information leakage by monitoring the disturbance of the transmitted quantum signals. Normally, the disturbance is reflected as bit flip errors in the sifted key; thus, privacy amplification, which removes any leaked information from the key, generally depends on the bit error rate. Recently, a round-robin differential-phase-shift QKD protocol for which privacy amplification does not rely on the bit error rate [Nature 509, 475 (2014)] was proposed. The amount of leaked information can be bounded by the sender during the state-preparation stage and hence, is independent of the behaviour of the unreliable quantum channel. In our work, we apply the tagging technique to the protocol and present a tight bound on the key rate and employ a decoy-state method. The effects of background noise and misalignment are taken into account under practical conditions. Our simulation results show that the protocol can tolerate channel error rates close to 50% within a typical experiment setting. That is, there is a negligible restriction on the error rate in practice.