Phys.org  January 24, 2022
As the photons carrying signals cannot be amplified or relayed via classical optical techniques to maintain quantum security, the transmission loss of the channel limits its achievable distance. An international team of researchers (Spain, Japan, Canada, China, Russia) has designed an experimental QKD system that could tolerate a channel loss beyond 140 dB and obtain a secure distance of 833.8 km. Furthermore, the optimized four-phase twin-field protocol and set-up make its secure key rate more than two orders of magnitude greater than previous records over similar distances… read more. TECHNICAL ARTICLE  1 ,  Open Access 2
Summary of recent long-distance QKD experiments beyond 400 km. Credit: Nature Photonics (2022)  Â