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21st June 2017

Entangled photons sent between suborbital space and Earth

Chinese scientists report the transmission of entangled photons between suborbital space and Earth, using the satellite Micius. More satellites could follow in the near future, with plans for a European–Asian quantum-encrypted network by 2020, and a global network by 2030.



In a landmark study, Chinese scientists report the successful transmission of entangled photons between suborbital space and Earth. Furthermore, whereas the previous record for entanglement distance was 100 km (62 miles), here, transmission over more than 1,200 km (746 miles) was achieved.

The distribution of quantum entanglement, especially across vast distances, holds major implications for quantum teleportation and encryption networks. Yet, efforts to entangle quantum particles – essentially "linking" them together over long distances – have been limited to 100 km or less, mainly because the entanglement is lost as they are transmitted along optical fibres, or through open space on land.

One way to overcome this issue is to break the line of transmission into smaller segments and repeatedly swap, purify and store quantum information along the optical fibre. Another approach to achieving global quantum networks is by making use of lasers and satellite technologies. Using a Chinese satellite called Micius, launched last year and equipped with specialised quantum tools, Juan Yin et al. demonstrated the latter feat. The Micius satellite was used to communicate with three ground stations across China, each up to 1,200 km apart.

The separation between the orbiting satellite and these ground stations varied from 500 to 2,000 km. A laser beam on the satellite was subjected to a beam splitter, which gave the beam two distinct polarised states. One of the spilt beams was used for transmission of entangled photons, while the other was used for photon receipt. In this way, entangled photons were received at the separate ground stations.

"It's a huge, major achievement," Thomas Jennewein, physicist at the University of Waterloo in Canada, told Science. "They started with this bold idea and managed to do it."

"The Chinese experiment is quite a remarkable technological achievement," said Artur Ekert, a professor of quantum physics at the University of Oxford, in an interview with Live Science. "When I proposed the entangled-based quantum key distribution back in 1991 when I was a student in Oxford, I did not expect it to be elevated to such heights."

One of the many challenges faced by the team was keeping the beams of photons focused precisely on the ground stations as the satellite hurtled through space at nearly 8 kilometres per second.

Quantum encryption, if successfully developed, could revolutionise communications. Information sent via this method would, in theory, be absolutely secure and practically impossible for hackers to intercept. If two people shared an encrypted quantum message, a third person would be unable to access it without changing the information in an unpredictable way. Further satellite tests are planned by China in the near future, with potential for a European–Asian quantum-encrypted network by 2020, and a global network by 2030.


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