Science

Lijiang observatory helps unravel mysteries of quantum communication

Lijiang observatory helps unravel mysteries of quantum communication”

The team beamed roughly six million pairs per second to separate telescopes on Earth from a satellite, The Wall Street Journal reports.

Once scoffed at by Einstein, quantum entanglement is a odd phenomenon that occurs when two or more particles link up and instantaneously affect each other, regardless of how far apart they are.

With the help of Micius - the world's first quantum-enabled satellite launched previous year - the researchers set out to communicate with three ground stations across China using entangled photons (light particles).

To send quantum signals farther, scientists have increasingly looked to the vacuum of space, which allows entangled photons to travel for hundreds or even thousands of kilometres before re-entering the atmosphere. But it's still a long, long time before we'll actually see this technology used in our communications networks.

Since then, scientists have witnessed and demonstrated quantum entanglement as a real phenomenon time and time again in laboratory settings. The satellite will overfly Beijing, establish a quantum key with a ground station, then establish another key with another station when it overflies Austria. For example, in 2012 researchers transported entangled photons about 146km apart from one another in the Canary Islands. Internet connections, for instance, remain vulnerable to online attacks, so quantum communication proves promising in forging faster, more secure communication channels.

One of the spilt beams was used for transmission of entangled photons, while the other was used for photon receipt. Ling is teaming up with physicists in Australia to send quantum information between two satellites, and the Canadian Space Agency recently announced funding for a small quantum satellite.

The idea is so counterintuitive that Albert Einstein mocked it as "spooky action at a distance". Regardless of the distance, the photons sustained their entanglement and were successfully received by the ground stations.

But despite China's latest achievement, the effort to build a useable quantum communications network still has a long way to go.

"In terms of quantum communications and satellite technology, certainly the Chinese are in front", said Ben Buchler, professor of physics at Australian National University. The main advantage of this approach is that most of the photons' transmission path is nearly in vacuum, with nearly zero absorption and de-coherence. They also hope to launch a quantum satellite to a higher orbit to make more practical use possible, according to Wang. Even transmission of only one pair with their quantum properties intact is sufficient to demonstrate that the concept is sound for quantum cryptography.

Central to QUESS's experiments is a laser beam mounted on the satellite.

The scientists are now working with satellite telecommunications company Tesat-Spacecom GmbH and others in the space industry to design a quantum network based on hardware already employed in space. "Today we pay bills: electrical bills, water bills", says coauthor Chao-Yang Lu, a physicist at the University of Science and Technology of China in Hefei.

Anton Zeilinger, a physicist at the Austrian Academy of Sciences in Vienna, told Science, "There are not many experiments which test links between gravity and quantum physics", he said.

In the new study, researchers used China's Micius satellite, which was launched a year ago, to transmit the entangled photon pairs.

Regarding quantum networking or internet, Jennewein described Thursday's quantum experiment result as "a very important milestone, because disseminating quantum entanglement is a first (and most important) building block". That's a big deal, and a major step toward a true quantum encryption system.



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