Plug-n-Play Three Pulse Twin Field QKD

TL;DR

This paper demonstrates a practical, stable, and scalable three-time-bin TF-QKD protocol using a Sagnac-based architecture, achieving secure key distribution over 50 km with real-time phase monitoring.

Contribution

It introduces a novel three-time-bin encoding scheme with a Sagnac loop that self-compensates for phase and polarisation drifts, enhancing real-world quantum communication.

Findings

Secure key rate of 1.5e-5 bits per pulse over 50 km

Achieved 87% interference visibility

Demonstrated system stability and scalability

Abstract

We present the experimental implementation of a three-time-bin phase-encoded Twin-Field Quantum Key Distribution (TF-QKD) protocol using a Sagnac-based star-topology plug-and-play architecture. The proposed encoding method leverages the relative phases of three consecutive time bins to encode two bits per signal. The Sagnac loop configuration enables self-compensation for both phase and polarisation drifts, eliminating the need for active stabilisation. However, field deployments are subject to rapid phase fluctuations caused by external vibrations, which can degrade interference visibility. We used the first time bin for real-time phase-fluctuation monitoring. Although this monitoring reduces the effective key generation rate, the system achieved a secure key rate of approximately 1.5e-5 bits per pulse, with a corresponding visibility of up to 87% over a 50 km asymmetric optical fibre channel. These results demonstrate the practicality, stability, and scalability of the proposed three-time-bin TF-QKD protocol for real-world quantum communication networks.