Twin-field quantum key distribution without phase locking

TL;DR

This paper introduces a practical TF-QKD method that eliminates the need for phase locking, simplifying long-distance quantum communication and achieving high secret key rates over standard optical fibers.

Contribution

The authors propose a novel no-phase-locking TF-QKD approach using reference and quantum frames with a fast Fourier transform algorithm for phase reconciliation.

Findings

Achieved high secret key rate of 1.27 Mbit/s at 50 km

Demonstrated repeater-like key rate scaling at 504 km

Enabled long-distance TF-QKD without phase locking hardware

Abstract

Twin-field quantum key distribution (TF-QKD) has emerged as a promising solution for practical quantum communication over long-haul fiber. However, previous demonstrations on TF-QKD require the phase locking technique to coherently control the twin light fields, inevitably complicating the system with extra fiber channels and peripheral hardware. Here we propose and demonstrate an approach to recover the single-photon interference pattern and realize TF-QKD \emph{without} phase locking. Our approach separates the communication time into reference frames and quantum frames, where the reference frames serve as a flexible scheme for establishing the global phase reference. To do so, we develop a tailored algorithm based on fast Fourier transform to efficiently reconcile the phase reference via data post-processing. We demonstrate no-phase-locking TF-QKD from short to long distances over standard optical fibers. At 50-km standard fiber, we produce a high secret key rate (SKR) of 1.27 Mbit/s, while at 504-km standard fiber, we obtain the repeater-like key rate scaling with a SKR of 34 times higher than the repeaterless secret key capacity. Our work provides a scalable and practical solution to TF-QKD, thus representing an important step towards its wide applications.