Discrete-phase-randomized mode-pairing quantum key distribution

TL;DR

This paper introduces a discrete-phase-randomized MP-QKD protocol that enhances practical security and performance, reducing randomness requirements and approaching continuous phase randomization with about 14 discrete phases.

Contribution

It proposes a discrete-phase version of MP-QKD, analyzes its security, and demonstrates that it nearly matches continuous phase performance with fewer random bits.

Findings

Key rate approaches continuous case at ~14 phases

Requires only a few random bits (e.g., 4) for security

Significantly reduces randomness demand compared to continuous phase randomization

Abstract

Mode-pairing quantum key distribution (MP-QKD) protocol achieves performance beyond the repeaterless rate-transmittance bound and exhibits excellent practicality by avoiding the requirement for difficult global phase locking. However, the source side of MP-QKD still relies on the assumption of continuous phase randomization, an experimentally infeasible requirement in practice. Therefore, the practical security of the protocol cannot be fully guaranteed. In this work, we propose a discrete-phase-randomized mode-pairing quantum key distribution (DPR-MP-QKD) protocol and analyze the basis-dependence of the source side. Then, we introduce a concrete discrete version of the decoy state method that ensures the security of the DPR-MP-QKD protocol. Finally, simulation results indicate that as the number of discrete phases increases, the key rate performance of DPR-MP-QKD progressively approaches that of the continuous case, with convergence achieved at approximately 14 discrete phases. Moreover, our approach drastically lowers the demand for randomness. While conventional continuous phase randomization demands an unlimited supply of random bits, we show that merely a few bits (e.g., 4) are adequate.