Coherent phase transfer for real-world twin-field quantum key distribution

TL;DR

This paper presents a novel interferometry-based method for stabilizing optical channels in twin-field quantum key distribution over long distances, enabling secure key exchange in real-world fiber networks.

Contribution

The authors introduce a coherent phase transfer technique that allows simultaneous key streaming and channel length control in long-distance quantum communication.

Findings

Successful demonstration over 206 km fiber with 65 dB loss

Quantum-bit-error-rate reduced to less than 1%

Effective stabilization method for real-world quantum networks

Abstract

Quantum mechanics allows the distribution of intrinsically secure encryption keys by optical means. Twin-field quantum key distribution is the most promising technique for its implementation on long-distance fibers, but requires stabilizing the optical length of the communication channels between parties. In proof-of-principle experiments based on spooled fibers, this was achieved by interleaving the quantum communication with periodical adjustment frames. In this approach, longer duty cycles for the key streaming come at the cost of a looser control of channel length, and a successful key-transfer using this technique in a real world remains a significant challenge. Using interferometry techniques derived from frequency metrology, we developed a solution for the simultaneous key streaming and channel length control, and demonstrate it on a 206 km field-deployed fiber with 65 dB loss. Our technique reduces the quantum-bit-error-rate contributed by channel length variations to <1%, representing an effective solution for real-world quantum communications.