July 23, 2017

Chinese scientists demonstrate quantum communication between space and ground stations

18 June 2017, 01:24 | Lucia Cruz

Jian-Wei Pan

Jian-Wei Pan

The lead author Juan Yin said, "We have demonstrated the distribution of two entangled photons from a satellite to two ground stations that are 1,203 kilometers apart".

The latter refers to entanglement-based quantum key distribution, which is so far the only way to establish secure keys between two distant locations on Earth without relying on trustful relay. Entangled photos are pairs of photos with linked properties and they remain that way even if they are separated by a distance. There's a lot less stuff to get in the way and destroy entangled particles when they're sent from space, so the particles can be transmitted across much greater distances.

Quantum entanglement is a phenomenon in quantum physics, which is so confounding that Albert Einstein described it as "spooky action at a distance" in 1948. That's because quantum mechanics states that measuring a quantum system inevitably disturbs it, so any attempt to eavesdrop is impossible to hide.

Pairs of entangled photons fired to ground stations can then form a 'secret key'.

Project leader Jian-Wei Pan, a physicist at the University of Science and Technology of China, proposed the project almost 15 years ago. They found the photons had opposite polarizations far more often than would be expected by chance, thus confirming spooky action over a record distance (though the 2015 test over a shorter distance was more stringent).

Anton Zeilinger, a physicist at the Austrian Academy of Sciences in Vienna and one of the first to propose the idea of a quantum internet, told Science the experiment "shows that China is making the right decisions". "So how can you do similar experiments at thousand-kilometers distance scale and with the optical elements vibrating and moving at a speed of 8 kilometers per second [5 miles per second]?"

The separation between the satellite and these ground stations varied from 310 to 1,243 miles (500-2,000 km).

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Scientists were absolutely floored by a groundbreaking discovery that could change our understanding of quantum physics.

. Essentially, entangled photons' sensitivity to interference can actually work to their advantage: when hackers try to steal the information, the signal immediately becomes unreadable and alerts the users to the presence of the hack.

That distance is 10 times greater than the previous record for entanglement. "It's very encouraging." However, Ling notes that Pan's team recovered only about one photon out of every 6 million sent from the satellite-far better than ground-based experiments but still far too few for practical quantum communication.

Other countries have joined the race for space-based quantum communication.

"I'm personally convinced that the internet of the future will be based on these quantum principles".

Above image: A solar wing deployment test for the experimental quantum communication satellite at the Jiuquan Satellite Launch Center in Jiuquan, northwest China's Gansu Province, July 30 2016. For one, its relatively low orbit means each ground station has coverage for only about 5 minutes each day, and the wavelength of photons used means it can only operate at night, he said. The obtained link efficiency is orders of magnitude higher than that of the direct bidirectional transmission of two photons through telecommunication fibers.

At its core, the technique is similar to encryption methods now used to protect information transmitted by Internet users, the British media outlet explained, but unlike that method, the new quantum-based technique hides the key required to unscramble the encrypted data in photons.

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