(PhysicsWorld) A network for quantum key distribution (QKD) spanning thousands of kilometres has been built in China. It links four quantum metropolitan area networks (QMANs) in cities in eastern China with a remote location in the far west of the country. The system comprises a 2000 km fibre optic link between the cities of Shanghai, Hefei, Jinan and Beijing and a satellite link spanning 2600 km between two observatories – one east of Beijing and the other just a few hundred kilometres from China’s border with Kazakhstan.
The network was built by Jian-Wei Pan at the University of Science and Technology of China in Hefei along with colleagues in academia and industry.
The Chinese network serves about 150 users and comprises more than 700 fibre links and two high-speed satellite-to-ground free-space links – all of which support QKD transmission. The fibre links are supported by 32 “trusted relay nodes” that are capable of forwarding quantum information. The individual QMANS contain trusted relay nodes as well as user nodes and optical switches. The Jinan QMAN is the largest, containing 50 user nodes supporting 95 users.
The satellite portion of the network makes use of the Micius quantum communications satellite, which was launched by China in 2016.

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