China’s quantum satellite in big leap – BBC News

 In Science

Launch of MiciusImage copyright
Getty Images

Image caption

Micius went up from the Jiuquan Satellite Launch Centre in China’s north west

The term “spy satellite” has taken on a new meaning with the successful test of a novel Chinese spacecraft.

The mission can provide unbreakable secret communications channels, in principle, using the laws of quantum science.

Called Micius, the satellite is the first of its kind and was launched from the Gobi desert last August.

It is all part of a push towards a new kind of internet that would be far more secure than the one we use now.

The experimental Micius, with its delicate optical equipment, continues to circle the Earth, transmitting to two mountain-top Earth bases separated by 1,200km.

The optics onboard are paramount. They’re needed to distribute to the ground stations the particles, or photons, of light that can encode the “keys” to secret messages.

“I think we have started a worldwide quantum space race,” says lead researcher Jian-Wei Pan, who is based in Hefei in China’s Anhui Province.

‘Messy business’

Quantum privacy in many ways should be like the encryption that already keeps our financial data private online.

Before sensitive information is shared between shopper and online shop, the two exchange a complicated number that is then used to scramble the subsequent characters. It also hides the key that will allow the shop to unscramble the text securely.

The weakness is that the number itself can be intercepted, and with enough computing power, cracked.

Quantum cryptography, as it is called, goes one step further, by using the power of quantum science to hide the key.

As one of the founders of quantum mechanics Werner Heisenberg realised over 90 years ago, any measurement or detection of a quantum system, such as an atom or photon of light, uncontrollably and unpredictably changes the system.

This quantum uncertainty is the property that allows those engaged in secret communications to know if they are being spied on: the eavesdropper’s efforts would mess up the connection.

Image copyright
NSSC

Image caption

Artwork: The two Earth stations are 1,200km apart

The idea has been developed since it was first understood in the 1980s.

Typically, pairs of photons created or born simultaneously like quantum twins will share their quantum properties no matter how long they are separated or how far they have travelled. Reading the photons later, by shopper and shop, leads to the numerical key that can then be used to encrypt a message. Unless the measurements show interference from an eavesdropper.

A network established in Vienna in 2008 successfully used telecommunications fibre optics criss-crossing the city to carry these “entangled photons”, as they are called. But even the clearest of optical fibres looks foggy to light, if it’s long enough. And an ambitious 2,000km link from Beijing to Shanghai launched last year needs repeater hubs every 100km or so – weak points for quantum hackers of the future to target.

And that, explains Anton Zeilinger, one of the pioneers of the field and creator of the Vienna network, is the reason to communicate via satellite instead.

“On the ground, through the air, through glass fibres – you cannot go much further than 200km. So a satellite in outer space is the choice if you want to go a really large distance,” he said.

The point being that in the vacuum of space, there are no atoms, or at least hardly any, to mess up the quantum signal.

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