Loophole-free plug-and-play quantum key distribution

TL;DR

This paper introduces a secure, practical plug-and-play quantum key distribution scheme that is robust, simple, and free of loopholes, demonstrated over 50 km of fiber with high stability and low error rate.

Contribution

It presents a loophole-free, two-way protocol for plug-and-play QKD with experimental validation over real-world fiber.

Findings

Achieved ultra-low error rate in QKD system

Maintained high visibility of 0.9947 over 24 hours

Demonstrated secure QKD over 50 km fiber

Abstract

Robust, simple, and flexible quantum key distribution (QKD) is vital for realising practical applications of this technique. Contrary to typical phase-coded QKD schemes, the plug-and-play QKD design requires only one arm-length-insensitive interferometer without active feedback, in which the noise is automatically compensated by the two-way structure. However, there are certain possible loopholes in the typical plug-and-play designs, which require consideration and strict monitoring. This study proposes a loophole-free plug-and-play QKD scheme with two-way protocol and presents an experimental demonstration of said scheme. The security is analysed under a collective attack scenario assisted by the decoy state method. The scheme was implemented in a 50.4 km commercial fibre without active feedback. The system showed highly robust performance with an ultra-low error rate and maintained an ultra-high visibility of 0.9947+/-0.0002 through significant environmental changes over 24 hours.