Curator's Take
AI Commentary
This article demonstrates the first three‑user twin‑field QKD network that operates over a 127 km Sagnac loop without any active phase stabilization or post‑compensation, showing that practical, multi‑node quantum cryptography can be built with relatively simple hardware. By achieving a stable interference visibility above 93 % and a secure key rate of 1.4 × 10⁻⁵ bits per pulse even on an asymmetric link with 45 dB loss, the work pushes TFQKD from point‑to‑point demos toward scalable metropolitan or intercity networks. The result suggests that cost‑effective, long‑distance quantum secure communications may soon be deployable using existing fiber infrastructure, though further improvements in key rate and robustness to real‑world traffic will be needed for commercial rollout.
— Mark Eatherly
Summary
Twin-field (TF) quantum key distribution (QKD) offers a promising approach to long-distance QKD networks due to its superior performance over large channel losses. Due to specialized hardware requirements, nearly all long-distance TFQKD demonstrations have only two users exchanging keys, rather than a network with three or more users. In this work, we experimentally demonstrate a proof-of-principle three-user-pair Sagnac TFQKD network spanning 127-km using single-photon avalanche detectors without any active phase stabilization or postcompensation. We implement efficient procedures for maintaining polarization stability and circumventing Rayleigh backscattering noise to achieve a stable Sagnac interference visibility of $93\pm1$% over one hour. A secure key rate of $1.398\times10^{-5}$ bits per pulse is achieved over an asymmetric communication channel with 102-km fiber and 45-dB overall loss. To our knowledge, this is the first TFQKD network without active phase stabilization or postcompensation achieved over long fibers. Our results represent a highly practical and cost-effective approach to long-distance QKD networks.