Quantum satellite shatters entanglement record

Geronimo Vena
Giugno 18, 2017

A Chinese quantum satellite has dispatched transmissions over a distance of 1,200 km (746 miles), a dozen times further than the previous record, a breakthrough in a technology that could be used to deliver secure messages, state media said on Friday.

Just months into its mission, the world's first quantum-communications satellite has achieved one of its most ambitious goals.

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).

The distribution of quantum entanglement, especially across vast distances, holds important implications for quantum teleportation and communication networks. As it soared over China, the satellite created pairs of photons with properties that were linked through quantum entanglement.

American and European teams are considering sending quantum-based equipment to the International Space Station. The team is likely to launch more quantum-enabled satellites to start building a network. With quantum entanglement such a basic requirement of quantum communication, "maybe someday we will need to pay some entanglement bills". Regardless of the distance, the photons sustained their entanglement and were successfully received by the ground stations.

Though the idea of using satellite relays to shunt entangled photons into space and back has always been considered, it wasn't until last August that the nation sent up its first such orbiter, the $100 million Quantum Experiments at Space Scale.

Quantum entanglement prompts philosophical discussions around quantum theory. This is done by doing a "Bell test", which determines whether correlations between the photons are stronger than that allowed by classical physics.

A laser beam on Micius was subjected to a beam splitter, which gave the beam two distinct polarized states. The pairs were split, with photons sent to separate receiving stations in Delingha and Lijiang, 1200 kilometers apart.

Ground-based Tests confirmed that the particles sent from the Micius satellite were indeed still entangled. 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. "By developing an ultra-bright space-borne two-photon entanglement source and high-precision APT, the team established entanglement between two single photons separated by 1203 km, with an average two-photon count rate of 1.1Hz and state fidelity of 0.869±0.085".

Zeilinger is working with Pan on an intercontinental quantum network and hopes to have results to report before the end of the year.

'You could not just see planets, ' Paul Kwiat, a physicist at the University of IL at Urbana-Champaign involved with the Nasa project, 'but in principle read licence plates on Jupiter's moons'.

"I have worked in this line of research since 2000 and researched on similar implementations of quantum- entanglement experiments from space, and I can therefore very much attest to the boldness, dedication and skills that this Chinese group has shown", he told Live Science. Essentially, this process can be used to instantly "teleport" information between them over theoretically infinite distances, which was Einstein's issue with the idea: it violated the law of general relativity that says nothing can travel faster than the speed of light.

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.

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