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

TLDR

Quantum mechanics enables intrinsically secure key distribution via optics, and twin‑field QKD is a promising approach for long‑distance fiber networks that requires precise channel‑length stabilization. The study aims to develop and demonstrate a frequency‑metrology‑based interferometric method that simultaneously streams keys and controls channel length over a 206 km field‑deployed fiber. The authors interleave quantum communication with periodic stabilization frames and employ interferometric techniques from frequency metrology to monitor and adjust the optical path length in real time. The technique reduces channel‑length‑induced QBER to below 1 %, demonstrating an effective real‑world solution.

Abstract

Quantum mechanics allows distribution of intrinsically secure encryption keys by optical means. Twin-field quantum key distribution is one of the most promising techniques for its implementation on long-distance fiber networks, 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 stabilization 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 real world remains a significant challenge. Using interferometry techniques derived from frequency metrology, we develop 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.