China's quantum satellite sends unbreakable signals from space

Lays the foundation for building a hack-proof global quantum communication network

China has sent an unbreakable code from its satellite to the Earth, laying the foundation for building a hack-proof global quantum communication network, official media said today.

The achievement based on experiments conducted with the world's first quantum satellite, Quantum Experiments at Space Scale (QUESS), was published in the authoritative academic journal Nature.

The Nature reviewers commented that the experiment was an impressive achievement, and constituted a milestone in the field, state-run Xinhua news agency reported.

Nicknamed "Micius," after a 5th Century BC Chinese philosopher and scientist who has been credited as the first person ever to conduct optical experiments, the 600-kilogram- plus satellite was sent into a sun-synchronous orbit at an altitude of 500 kilometers on August 16, 2016.

Pan Jianwei, the lead scientist of QUESS and an academician of the Chinese Academy of Sciences (CAS), said the satellite sent quantum keys to ground stations in Xinglong, in north China's Hebei Province, and Nanshan, near Urumqi, the capital of northwest China's Xinjiang Uygur Autonomous Region.

The communication distance between the satellite and the ground station varies from 645 kilometres to 1,200 kilometres, and the quantum key transmission rate from satellite to ground is up to 20 orders of magnitude more efficient than that expected using an optical fibre of the same length, said, Pan.

When the satellite flies over China, it provides an experiment window of about 10 minutes. During that time, the 300 kbit secure key can be generated and sent by satellite, according to Pan.

"That, for instance, can meet the demand of making an absolute safe phone call or transmitting a large amount of bank data," Pan said.

"Satellite-based quantum key distribution can be linked to metropolitan quantum networks where fibres are sufficient and convenient to connect numerous users within a city over 100 km. We can thus envision a space-ground integrated quantum network, enabling quantum cryptography-most likely the first commercial application of quantum information- useful at a global scale," Pan said.

The establishment of a reliable and efficient space-to-ground link for faithful quantum state transmission paves the way to global-scale quantum networks, he added.