(PhysicsWorld) Continuous-variable quantum key distribution (CV-QKD) systems in China have shattered distance and speed records when implemented on commercial fibre networks. Operating in two cities, the systems distributed cryptography keys up to 50 km (three times further than the previous record) and with secret-key transmission rates more than 100 times faster than previous systems.
In this latest demonstration, Hung Guo, Yichen Zhang, Song Yu and colleagues at Peking University and Beijing University of Posts and Telecommunications operated CV-QKD systems in Xi’an and Guangzhou using commercial fibre links. In both cases the links were “dark”, which means that they carried no other telecoms traffic during the tests.
In Xi’an the team transmitted secret keys a distance of 30 km, whereas nearly 50 km transmission was achieved in Guangzhou – smashing the previous record of just over 17 km for CV-QKD over commercial fibre. Although quantum cryptography has previously been achieved over distances of hundreds of kilometres, these demonstrations were done on dedicated fibres rather than on commercially-deployed telecoms links.

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