The Chinese team of physicists who have demonstrated quantum key distribution between satellite and Observatory for the first time had a session of quantum cryptography using entanglement between two ground stations at a distance of 1120 miles. The work presented in the journal Nature.
Quantum distribution key is theoretically secure way of sharing secret keys between remote users. The method is based on the fundamental laws of quantum physics: the process of measuring a quantum system changes its state. An attacker who tries to steal the key must in some way measure it, but measuring introduces anomalies that I see and the legitimate participants of the Protocol. Thus, users can open and test the portion of the key and make sure that no one, except themselves, was not measured.
The experimental distribution of the key was demonstrated in the laboratory by means of optical fibers with a length of 421 kilometers. Previously, we wrote outside the lab Chinese scientists led by Professor Jian-Wei pan (Jian-Wei Pan) managed to transfer the key from the satellite to the ground station at a distance of 1200 kilometers, which today is an absolute record.
However, the real cryptography based on quantum key distribution aimed at users that are on Earth. When using quantum repeaters, you can create a network of nodes that are at a distance of up to 100 kilometers from each other. Unfortunately, each repeater carries a security risk and can be attacked by an attacker. Another method of key distribution over large distances uses satellite communication using quantum entanglement.
The same group of Chinese scientists led by Professor pan for the first time had a session of quantum key distribution based on entanglement between two ground stations, the distance between which amounted to 1120 kilometers. Entangled pair of photons were separated and sent via communication channels from satellites Micius to two ground-based observatories in Delingha (Delhi) and Nanshan (Nanshan).
Important engineering achievement, without which the experiment would not have taken place, is the establishment of a highly efficient telescope and optics manufacturing. Scientists were able to increase the collection efficiency data for each communication channel of the satellite-Earth about two times compared to the previous experiment. The best data were obtained on a clear night and no fog when the atmosphere had the highest transmittance.