Independent Optical Frequency Combs Powered 546 km Field Test of Twin-Field Quantum Key Distribution

TL;DR

This study demonstrates the practical viability of twin-field quantum key distribution over long distances using independent optical frequency combs in real-world field conditions, achieving secure key rates over 546 km.

Contribution

First field demonstration of independent optical frequency combs for twin-field QKD over 546 km, enabling network-friendly, long-distance secure communication without optical frequency dissemination.

Findings

Achieved secure key rate of 0.53 bit/s over 546 km

Supported 44 km fiber asymmetry in a 452 km link

Demonstrated feasibility of long-haul quantum networks

Abstract

Owing to its repeater-like rate-loss scaling, twin-field quantum key distribution (TF-QKD) has repeatedly exhibited in laboratory its superiority for secure communication over record fiber lengths. Field trials pose a new set of challenges however, which must be addressed before the technology's roll-out into real-world. Here, we verify in field the viability of using independent optical frequency combs -- installed at sites separated by a straight-line distance of 300~km -- to achieve a versatile TF-QKD setup that has no need for optical frequency dissemination and thus enables an open and network-friendly fiber configuration. Over 546 and 603 km symmetric links, we record a finite-size secure key rate (SKR) of 0.53~bit/s and an asymptotic SKR of 0.12 bit/s, respectively. Of practical importance, the setup is demonstrated to support 44~km fiber asymmetry in the 452 km link. Our work marks an important step towards incorporation of long-haul fiber links into large quantum networks.