Security of quantum key distribution with imperfect phase randomisation

TL;DR

This paper proves the security of decoy-state quantum key distribution even when phase randomisation is imperfect and phases are correlated, enabling more practical and high-performance secure quantum communication.

Contribution

It provides a novel security proof for decoy-state QKD with correlated phases, approaching ideal key rates despite practical phase correlations.

Findings

Security proof for correlated phase QKD

Key rates close to ideal with imperfect phase randomisation

Enables practical high-speed QKD implementations

Abstract

The performance of quantum key distribution (QKD) is severely limited by multiphoton emissions, due to the photon-number-splitting attack. The most efficient solution, the decoy-state method, requires that the phases of all transmitted pulses are independent and uniformly random. In practice, however, these phases are often correlated, especially in high-speed systems, which opens a security loophole. Here, we address this pressing problem by providing a security proof for decoy-state QKD with correlated phases that offers key rates close to the ideal scenario. Our work paves the way towards high-performance secure QKD with practical laser sources, and may have applications beyond QKD.