In long-distance practical applications of quantum key distribution (QKD), channel loss is the most serious limiting factor. The existing measurement equipment-independent quantum key distribution (MDI-QKD) uses a two-photon composite event as an effective detection event, so that its secure coding rate decreases linearly with the channel attenuation.

In two related studies, PAN Jianwei and colleagues at the University of Science and Technology in China developed a time-frequency transmission technology and a laser injection locking technology based on a “send-not-send” TF-QKD and a PM-QKD. The wavelength locks of two independent remote lasers are the same, and the additional phase reference light is used to estimate the relative phase drift of the fiber. Combined with the high counting rate and low noise single photon detector developed by CAS Shanghai Institute of Microsystem and Information Technology, QKD’s safe coding distance was finally pushed to over 500 kilometers in the laboratory. 

CAS news release, March 4, 2020

© PAN Jianwei et al.