China launches world's first quantum satellite

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The QUESS satellite being launched on a Long March-2D rocket(Credit: Xinhua/Jin Liwang)

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A Chinese orbiter launched atop a Long March-2D rocket is claimed to be the world's first quantum communications satellite earlier this week. According to Xinhua, the 600-kg (1,320-lb) Quantum Experiments at Space Scale (QUESS) satellite will sit in a sun-synchronous orbit above the Earth at an altitude of around 500 km (310 mi) from where it will transmit quantum-encrypted messages, attempt to send beam entangled photons, and test teleportation between itself and stations on the ground.

Designed to carry out its mission over the next two years, the QUESS satellite (nicknamed "Micius" in honor of a Chinese philosopher and scientist who lived in the fifth century BCE and is claimed to be one of the very first to conduct optical experiments) will help Chinese scientists run experiments on quantum key distribution between the orbiter and Earth stations, as well as test the ability to maintain secure quantum communications between Beijing and Urumqi – the capital of the Xinjiang Uyghu region in Northwest China.

"The newly-launched satellite marks a transition in China's role – from a follower in classic information technology (IT) development to one of the leaders guiding future IT achievements," said Pan Jianwei, chief scientist of the QUESS project at the Chinese Academy of Sciences (CAS).

Quantum key encryption is quickly becoming an established method of ultra-secure communication, particularly as any attempt to intercept or read the encoded information means that the quantum state of the key will immediately collapse and render the data unreadable. This is because photons encoded with a particular spin state (the quantum representation of binary-encoded data) is applied, then it cannot then be measured again, unless a specific encryption "key" is applied to it which is of the same value as the one that measured its spin state in the first place.

Though the quantum communications distance record currently sits at about 100 km (62 miles) over optical fiber, Chinese scientists say they plan to attempt an even greater feat by transmitting entangled photons from Earth orbit. Given that the largest impediment to transmission length is the eventual scattering of photons within the optical fiber, and that the Earth's atmosphere is particularly effective at dispersing light, this will be a challenging feat.

Further complicating this experiment will be the fact that the satellite will be traversing the sky at around 8 km/s (17,895 mph), and only able to be continually monitored by the ground station for a few minutes at a time. It will also require an alignment with QUESS that is some 10 times more accurate than normal quantum detectors, especially as, according to the CAS scientists, they expect to intercept just one in every million entangled photons beamed from the satellite.

"It will be like tossing a coin from a plane at 100,000 meters above the sea level exactly into the slot of a rotating piggy bank," said Wang Jianyu, QUESS project's chief commander.

According to Jianwei, the interest in long-distance quantum key distribution and its future development means that experiments between QUESS and participating Earth stations in Austria, Germany, Italy, and Canada are planned. All going well, the successful use of QUESS in collaboration with such international participants could lead Chinese scientists to develop a full-blown ground-to-satellite quantum communication system, with the intention of enabling worldwide quantum communications, further research on quantum control and light transmission from space, as well as tests on quantum communications between satellites.

"If China is going to send more quantum communication satellites into orbit, we can expect a global network of quantum communications to be set up around 2030," said Pan.

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