Researchers report an experimental demonstration of a space-to-ground quantum key distribution (QKD) network using a compact QKD terminal aboard the Chinese Space Lab Tiangong-2 and four ground stations. The new QKD system is less than half the weight of the system the researchers developed for the Micius satellite, which was used to perform the world's first quantum-encrypted virtual teleconference.

The demonstration represents an important step toward practical QKD based on constellations of small satellites, a setup considered one of the most promising routes to creating a global quantum communication network.

"QKD offers unconditional security by using single photons to encode information between two distant terminals," said research team member Cheng-Zhi Peng from the University of Science and Technology of China. "The compact system we developed can reduce the cost of implementing QKD by making it possible to use small satellites."

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