Twin-field quantum key distribution over 830-km fibre

Quantum key distribution (QKD) provides a promising solution for sharing information-theoretic secure keys between remote peers with physics-based protocols. According to the law of quantum physics, the photons carrying signals cannot be amplified or relayed via classical optical techniques to maintain quantum security. As a result, the transmission loss of the channel limits its achievable distance, and this has been a huge barrier towards building large-scale quantum-secure networks. Here we present an experimental QKD system that could tolerate a channel loss beyond 140 dB and obtain a secure distance of 833.8 km, setting a new record for fibre-based QKD. Furthermore, the optimized four-phase twin-field protocol and high-quality set-up make its secure key rate more than two orders of magnitude greater than previous records over similar distances. Our results mark a breakthrough towards building reliable and efficient terrestrial quantum-secure networks over a scale of 1,000 km. Twin-field (TF) quantum key distribution (QKD) over a secure distance of 833.8 km is demonstrated even in the finite-size regime. To this end, an optimized four-phase TF-QKD protocol and a high-speed low-noise TF-QKD system are developed.

Automated summary

The research team presents an experimental QKD system that can tolerate channel loss and achieve a secure distance of 833.8 km, setting a new record for fibre-based QKD. The optimized protocol and high-quality setup result in a significantly higher secure key rate compared to previous records over similar distances. This breakthrough marks a significant step towards establishing reliable and efficient terrestrial quantum-secure networks over a scale of 1,000 km.