Experiment With Chinese Satellite Demonstrates Quantum Weirdness Over Record Distances

Jian-Wei Pan

Jian-Wei Pan

The field of quantum cryptography, which seeks to transmit encrypted information using entangled quantum particles like photons, could help lay the groundwork for tomorrow's quantum networks but it faces a significant physical hurdle: entangled photons are insane hard to transmit long distances.

The feat, published today in the journal Science, is more than 10 times the distance previously achieved using land-based fibre optic technologies.

Led by Pan Jianwei, a quantum physicist at the University of Science and Technology of China, the team generated a pair of entangled photons on Micius and distributed one to a receiving station in Delingha and the other to a station in Lijiang.

Quantum entanglement has interesting applications for testing the fundamental laws of physics, but also for creating exceptionally secure communication systems, scientists have said.

Though it sounds like a pointless exercise to make "twin" particles and send them careening away from each other, scientists are doing just that in order to pioneer what's called "quantum communication", an ultra-private way of sending messages. Recognizing this, Pan proposed that entangled particles sent through space could vastly extend the distance across which entangled particles communicate. The satellite had placed a system of mirrors, lasers, and a special crystal on board, according to Wired.

The 1,300 pound craft satellite is equipped with a laser beam, which the scientists subjected to a beam splitter.

One of the spilt beams was used for transmission of entangled photons, while the other was used for photon receipt. Then he wants to demonstrate intercontinental quantum key distribution between stations in China and Austria, which will require holding one half of an entangled photon pair on board until the Austrian ground station appears within view of the satellite.

He said that among what Chinese researchers plan to do next is to expand satellite coverage so as to accomplish round-the-clock quantum communications.

One way to improve particle distribution is to break the transmission line into smaller sections, and then swap, purify, and store the quantum information along the optical fibre. This cryptography typically uses long numbers as a key to scrambling and unscrambling the data.

A cornerstone of quantum physics is a process called entanglement, where the properties of two particles - such as spin, position and momentum - intimately affect each other, even when those particles are separated by large distances.

But no light gets absorbed in space, because there's nothing to do the absorbing.

Photons are extremely fragile: they travel more smoothly in the near vacuum of space than in the earth's atmosphere.

China made history by successfully shooting a hack-proof quantum signal from space that smashed previous records on the transmission of such entangled particles.

The development of the satellite is part of the larger plan to developing a new kind of internet that is more secure that what is now used. Aiming is also a challenge because of the high speeds of the satellite and its distance to the ground.

Micius forms part of a wider Quantum Experiments at Space Scale (QESS) study.

This experiment would attempt to create a reliable and efficient means for teleportation.

"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 Wilfred Laurier University in Canada, according to The Washington Post.

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