Xinhua quoted Pan Jianwei, lead scientist of the project QUESS and an academician of the Chinese Academy of Sciences (CAS), saying the satellite sent quantum keys to ground stations in Xinglong, in north China's Hebei Province, and Nanshan near Urumqi, capital of northwest China's Xinjiang Uygur Autonomous Region.
The form of key distribution (think of it as a unique random password only known to the sender and receiver) has been branded "hack-proof", because any tampering would be noticed due to the fact it permanently disturbs the communication.
Scientists are conducting quantum key distribution experiments with a ground station in Graz, Austria.
In the first trial of a communication system created to be hack-proof, China has sent a stream of quantum encryption keys from a satellite to earth.
There are also plans for China to launch more quantum satellites, with the aim of establishing an orbiting "constellation". "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". So Chinese scientists have to acquire the technology to enable space-based quantum communication in the daytime, Peng said.
In the latest experiment by Chinese scientists, quantum states of photons were transmitted from a ground station (located in Ali Prefecture in Tibet) to Micius satellite. And if we have a satellite in orbit at 36,000 kilometers, it can cover a third of the earth all the time. Most in the field agree that national, worldwide and global quantum networks will require data to be sent at least partially via satellites because traditional media such as fiber cable results in too much interference and data loss.
"Satellite-based quantum key distribution can be linked to metropolitan quantum networks where fibers are sufficient and convenient to connect numerous users within a city over 100 km", Pan told Xinhua.
An arbitrary unknown quantum state can not be precisely measured or perfectly replicated1.
Long-distance teleportation is considered a fundamental element in protocols involving distributed quantum computation and large-scale quantum networks. To optimize the link efficiency and overcome the atmospheric turbulence in the up-link, a series of techniques are developed, including a compact ultra-bright source of multi-photon entanglement, narrow beam divergence, high-bandwidth and high-accuracy acquiring, pointing and tracking (APT).
This work established the first ground-to-satellite uplink for faithful and ultra-long-distance quantum teleportation, an essential step toward a global-scale quantum Internet, Pan said.
The limit for quantum teleportation is constantly expanding.