Field-Trial Quantum Key Distribution with Qubit-Based Frame Synchronization
Rui Guan, Jingchun Yu, Zhaoyun Li, Hongbo Xie, Yuxing Wei, Sen Li, Jing Wen, Xiaodong Liang, Yanwei Li, and Kejin Wei

TL;DR
This paper demonstrates a practical, long-term quantum key distribution system using qubit-based frame synchronization over urban fiber networks, achieving high stability, low error rates, and secure key rates without extra hardware.
Contribution
It introduces a novel qubit-based frame synchronization method for QKD, eliminating the need for dedicated synchronization hardware in real-world urban environments.
Findings
Achieved a secure key rate of 26.6 kbit/s at 18 dB loss.
Maintained a low QBER of 1.12% over 12 hours of continuous operation.
Validated the system's stability and high-loss tolerance in a real urban setting.
Abstract
Quantum key distribution (QKD) is a cryptographic technique that uses quantum mechanical principles to enable secure key exchange. Practical deployment of QKD requires robust, cost-effective systems that can operate in challenging field environments. A major challenge is achieving reliable clock synchronization without adding hardware complexity. Conventional approaches often use separate classical light signals, which increase costs and introduce noise that degrades quantum channel performance. To address this limitation, we demonstrate a QKD system incorporating a recently proposed qubit-based distributed frame synchronization method, deployed over a metropolitan fiber network in Nanning, China. Using the polarization-encoded one-decoy-state BB84 protocol and the recently proposed qubit-based distributed frame synchronization method, our system achieves synchronization directly from…
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