It is all part of a push towards a new kind of internet that would be far more secure than the one we use now. The experimental Micius, with its delicate optical equipment, continues to circle the Earth, transmitting to two mountain-top Earth bases separated by 1,200km.
The optics onboard are paramount. They're needed to distribute to the ground stations the particles, or photons, of light that can encode the "keys" to secret messages.
"I think we have started a worldwide quantum space race," says lead researcher Jian-Wei Pan, who is based in Hefei in China's Anhui Province.
A successful quantum communication network will rely on the ability to distribute entangled photons over large distances between receiver stations. So far, free-space demonstrations have been limited to line-of-sight links across cities or between mountaintops. Scattering and coherence decay have limited the link separations to around 100 km. Yin et al. used the Micius satellite, which was launched last year and is equipped with a specialized quantum optical payload. They successfully demonstrated the satellite-based entanglement distribution to receiver stations separated by more than 1200 km.