Tuesday, 24 October, 2017

Chinese scientists use satellite to smash quantum entanglement distance record

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Garry Little | 18 June, 2017, 01:27

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


The current satellite is not quite ready for use in practical quantum communication systems, though, according to Pan.

Quantum physicists have a fundamental interest in distributing entangled particles over increasingly long distances and studying the behaviour of entanglement under extreme conditions. The stations were located 1,203 kilometres apart, a ten-fold increase over similar ground-based experiments. That means you could know whether the other one was heads or tails by simply flipping your own coin. Previous experiments encased the photons in an optical fiber to protect them, passing the message down the line from particle to particle. Image courtesy of 中科大 (University of Science and Technology of China).

Although these experiments generated roughly 5.9 million entangled pairs of photons every second, the researchers only detected about one pair per second.

This experiment was made through two satellite-to-ground downlinks with a summed length varying from 1600-2400 km. The complex physics phenomenon was once even scoffed at by Albert Einstein, who dismissed it as "spooky action at a distance."However, new research now indicates that not only is quantum entanglement possible theoretically but it can also be demonstrated practically and could be the harbinger of a complete quantum satellite communication network".

One way to improve the distribution lies in the protocol of quantum repeaters, whose practical usefulness, however, is hindered by the challenges of quantum storage and readout efficiency, Pan said.

The researchers say that satellite-based entanglement distribution could be used to implement quantum key distribution (QKD) on a global scale.

The key advantage of a space-based approach is that most of the interference that entangled photons face occurs in the lower 10 kilometers or so of the atmosphere. The feat showed that the particles of light can retain a odd type of interconnectedness, known as quantum entanglement, even when flung to opposite ends of a country, researchers from China report in the June 16 Science.

"The experiment shows that long-range quantum communication is indeed technologically feasible and holds out the promise of the construction of long-range quantum communication networks in the near future", Xinhua quoted Lloyd as saying.

This time around, however, the Chinese team used their newly-launched Micius satellite, which allowed them to send the photons unobstructed through the void of space. It then beamed these simultaneously to ground stations in Delingha, Lijiang and Nanshan.

As per Science Daily, each station was about 1200 km apart and within 500 to 2000 km away from the orbiting satellite.

"It's a really stunning achievement, and I think it's going to be the first of possibly many such interesting and exciting studies that this particular satellite will open up", said Shohini Ghose, a physicist at Wilfrid Laurier University in Canada. To optimize link efficiency, the scientists combined narrow-beam divergence with a high-bandwidth and high-precision acquiring, pointing, and tracking (APT) technique.

"Using the distributed entangled photons, we performed the Bell test at spacelike separation and without the locality and the freedom-of-choice loopholes".

Quantum entanglement - or what Einstein used to call "spooky action at a distance" - is a physical phenomenon that occurs when pairs or groups of particles are generated or interact in ways such that the quantum state of each particle can not be described independently of the others.


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