Invited: Towards practical long-distance quantum communication — Twin-field QKD (Chair: Xiangbin Wang)

Abstract: Quantum key distribution (QKD) enables two remote parties to communicate with information-theoretic security. While QKD has been developed as the most mature technology in quantum communication application, it was still very challenging to practically extend the communication distance of QKD systems beyond the repeaterless limit. Twin-field (TF) QKD protocols overcame this challenge and can beat the fundamental rate-loss limit at high loss regimes. However, experimental implementations of TF QKD have been challenging, due to its requirement of phase stability over very long fiber distances. Here, we review the progress on improving the rate-loss limit for QKD over the past decades, and present the latest efforts in experimental demonstration of TF-QKD. Especially, I will introduce our method where a Sagnac loop structure is utilized to automatically compensate the phase fluctuations in fibers linking the various parties, which not only removes the need of phase stabilization, but also allows large asymmetric location of the users from the central measurement station. A multi-user TFQKD network, a first, is also presented here.