Twin-field quantum key distribution with discrete-phase-randomized sources

TL;DR

This paper proposes a practical variant of twin-field quantum key distribution using discrete-phase-randomized sources, demonstrating it can surpass the rate-loss bound and align closely with ideal continuous-phase schemes.

Contribution

It introduces a discrete-phase-randomized source scheme for TF-QKD, proving its security and showing it nearly matches continuous-phase performance in overcoming rate-loss limits.

Findings

Discrete-phase sources can surpass the rate-loss bound.

Performance approaches that of continuous-phase sources with few phases.

Security against collective attacks is established.

Abstract

Thanks to the single-photon interference at a third untrusted party, the twin-field quantun key distribution (TF-QKD) protocol and its variants can beat the well-known rate-loss bound without quantum repeaters, and related experiments have been implemented recently. Generally, quantum states in these schemes should be randomly switched between the code mode and test mode. To adopt the standard decoy-state method, phases of coherent state sources in the test mode are assumed to be continuously randomized. However, such a crucial assumption cannot be well satisfied in experimental implementations. In this paper, to bridge the gap between theory and practice, we propose a TF-QKD variant with discrete-phase-randomized sources both in the code mode and test mode, and prove its security against collective attacks. Our simulation results indicate that, with only a small number of discrete phases, the performance of discrete-phase-randomized sources can overcome the rate-loss bound and approach that of continuous-phase-randomized sources.