Jianyong Hu

The twin-field (TF) quantum key distribution (QKD) protocol and its variants are highly attractive because they can beat the well-known fundamental limit of secret key rate for point-to-point (point-to-point bound) QKD without quantum repeaters. In this paper, we perform a proof-of-principle experimental demonstration of TF-QKD based on the protocol proposed by Curty et al., which removes the need for post-selection on the matching of a global phase from the original TF-QKD. Furthermore, we employ a Sagnac loop structure to overcome the major difficulty in the practical implementation of TF-QKD, namely, the need to stabilize the phase of the quantum state over kilometers of fiber. The experimental results show that the secret key rate of TF-QKD at high loss region can surpass the point-to-point bound of QKD with current technology.