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takyon writes:

Quantum Satellite Links Extend More Than 1,000 Kilometers

A space-based, virtually unhackable quantum Internet may be one step closer to reality due to satellite experiments that linked ground stations more than 1,000 kilometers apart, a new study finds.

[...] In 2017, scientists in China used the satellite nicknamed Micius, which is dedicated to quantum science experiments, to connect sites on Earth separated by up to roughly 1,200 kilometers via entanglement. Although those experiments generated about 5.9 million entangled pairs of photons every second, the researchers were able to detect only one pair per second, an efficiency rate far too low for useful entanglement-based quantum cryptography.

Now, the same researchers have achieved their goal of entanglement-based quantum cryptography using the Micius satellite. The scientists, who detailed their findings [DOI: 10.1038/s41586-020-2401-y] [DX] online in the 15 June edition of the journal Nature, say they again connected two observatories separated by 1,120 kilometers. But this time, the collection efficiency of the links was improved by up to four-fold, which resulted in data rates of about 0.12 bits per second.

The scientists employed two ground stations, in Delingha and Nanshan, in China. Each site had a newly built telescope 1.2 meters wide that was specifically designed for the quantum experiments.

To boost the efficiency of the quantum cryptography links, the researchers focused on improving the systems used to acquire, orient toward and track targets at both the satellite and ground stations. They also made sure to improve the receiving and collection efficiencies of the lenses and other optical equipment on the ground.

Also at New Scientist and NYT.

Previously: China's "Quantum-Enabled Satellite" Launches
China's Quantum Communications Satellite Beats Record
Unbreakable: China Doubles Down On Quantum Internet
Quantum Video Chat Links Scientists on Two Different Continents
Why This Intercontinental Quantum-Encrypted Video Hangout is a Big Deal

Related: Quantum Ghost Imaging Spy Satellites

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