Quantum breakthrough from Chinese satellite mission could improve communications security

18 June, 2017, 01:26 | Author: Lorena Waters
  • Jian-Wei Pan

Now, a team led by Jian-Wei Pan of the University of Science and Technology of China in Hefei has used the photon source to distribute entangled photons to pairs of three ground stations in China - each up to 1200 km apart.

A report published by Washington Post informed, "The behavior of entangled particles in space and across vast distances offers insight into the nature of space-time and the validity of Einstein's theory of general relativity". This "spooky action at a distance", as some are calling it, would be like if you flipped two coins and no matter where on Earth they landed, one would end up heads and the other tails.

The 600-kilogram payload now onboard the Chinese satellite that is producing pairs of quantum entangled photons. Of the six million or so entangled pairs generated by Micius during each second of transmission, only one pair per second actually reached the ground-based detectors. "Doing them between two remote ground locations and a satellite flying overhead at a speed of thousands of kilometres per hour is mind-bogglingly hard".

Quantum entanglement has interesting applications for testing the fundamental laws of physics, but also for creating exceptionally secure communication systems, scientists have said. So far, entanglement distribution has only been achieved at a distance up to ~100 km due to photon loss in optical fibers or terrestrial free space.

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.

Fortunately, Yin and his team have just demonstrated a better way for achieving global quantum networks using laser beams and satellite technology. 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. The feat showed that the particles of light can retain a unusual 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 idea is that two parties who wish to communicate are sent one half of the pair.

The entanglement distribution satellite, called Micius, was launched in August past year. The distance between Delingha and Lijiang (Nanshan) is 1203 km.

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Each of the stations were around 1,200 kilometres apart and between 500 to 2,000 kilometres away from the orbiting satellite.

'In the next five years we plan to launch some really practical quantum satellites, ' Pan said, speaking to Science.

"To optimise link efficiency, the scientists combined narrow-beam divergence with a high-bandwidth and high-precision acquiring, pointing, and tracking [APT] technique", said the Academy.

The Chinese team has called this technology "the the only way to establish secure keys between two distant locations on earth without relying on trustful relay". The scientists found that photons retained their entangled states during their journey to Earth.

The work obliterates the previous world record for sending pairs of photons that are connected to one another by a unusual rule of quantum physics first spotted by Einstein.

Entanglement involves putting objects in the peculiar limbo of quantum superposition, in which an object's quantum properties occupy multiple states at once: like Schrödinger's cat, dead and alive at the same time. Another immediate application is to exploit distributed entanglement to perform a variant of quantum teleportation protocol for remote preparation and control of quantum states.

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