China makes quantum leap with Mozi satellite

China makes quantum leap with Mozi satellite 2

A day after its launch, world's first quantum communication satellite has sent 202 MB of good quality data to the China Remote Sensing Satellite Ground Station (RSGS), located near Beijing. The project, initiated by the Chinese Academy of Sciences in 2008, tests a technology that could one day offer digital communication that is "hack-proof".

On Tuesday, August 16th a Long March 2D rocket blasted off from the Jiuquan Launch Centre in the Gobi desert and brought the 500 kilogram satellite, equipped with a quantum entanglement generator and a high-speed laser communicator, in its orbit at an altitude of 600 km. Officially known as the Quantum Science Satellite (QSS), the mission has been renamed "Mozi," after a  Chinese scientist and philosopher who lived in the 5th century BC.

Mozi drawing2Mozi, or Micius in Latin, discovered that light travels in straight lines more than 2,000 years ago and was likely the first person to record an image with a pinhole. He was an extremely skilled carpenter and designed everything, from mechanical birds to wheeled, mobile "cloud ladders" used to besiege city walls. Mozi was no fan of Confucius and his philosophies emphasized self-reflection and authenticity rather than obedience to ritual.

"Just like the Galileo satellites and Kepler telescopes, we used the name of a famous scholar for our first quantum satellite. We hope this will promote and boost confidence in Chinese culture," said Pan Jian-Wei, the project’s chief scientist.

Pan's former professor at the University of Vienna, physicist Anton Zeilinger, first proposed the idea to the European Space Agency, without success, in 2001. He is now also participating in this mission, designed to be operational for up to two years, with Austria's Academy of Sciences providing the optical receivers for the ground stations in Europe.

Mozi's first mission is to establish "hack-proof" quantum communications. A message would be encrypted by a unique cryptographic key chain in Beijing and sent to Vienna through a conventional telecommunications network. At the same time, a special kind of laser would beam the key chain to the quantum satellite in the form of photons with various quantum properties such as clockwise or counterclockwise spins.

The satellite will then create pairs of so-called entangled photons beaming one half of each pair down to the base stations in China and Austria in order to establish secure quantum channels that allow the receiver in Vienna to decipher the message. Due to the "observer effect", which means that quantum properties cannot be measured or cloned without destroying the particle’s original quantum states, the cryptographic keys could not be stolen as any interception would be obvious and would also change the key, making it useless.

Fibre-optic quantum key networks already exist in Europe, the US and China, but the signals weaken over distance, which this project is hoping to minimise by sending the signals mostly through space, keeping attenuation to a minimum despite the distances involved. If it works, it will solve the central problem of encrypted communications - how to distribute keys without interception - promising truly secure encryption.

Mozi's second mission is to find out more about the entanglement of particles, one of the most intriguing elements of quantum theory. If two particles are entangled, the change of quantum state on one particle would immediately trigger a counter-change on the other. In theory, the entanglement would occur regardless of the distance between the particles, but the greatest distance of entanglement achieved on the ground, by Professor Pan, is only 100 km.

Mozi will seek to improve on that by an order of magnitude, beaming one entangled photon to a ground station in Delingha, Tibet, and the other to a station in Lijiang in Yunnan or Nanshan in Xinjiang, to see if the entanglement can be maintained between two ground stations more than 1,000 km apart. If the results of the second mission are positive, the satellite’s third mission will take quantum theory to its most exciting application: quantum teleportation in space.

Researchers will generate a pair of entangled photons at a ground station. One photon will be beamed to the satellite, the other kept on the ground. Then, the scientists will alter the quantum state of the particle on the ground, such as giving it a clockwise spin. A detector on the satellite will tell if a counterclockwise spin occurs simultaneously on the particle in space.

More information: Physicists prove 'quantum spookiness' and chase Schrödinger’s cat

Many problems remain to be solved, such as maintaining the entangled state of quantum particles during their long-distance space flight. To beam a single photon from the satellite to a one-metre-wide telescope on the ground, or to catch a single photon from the ground with a satellite moving at 7,500km/h, with rain, clouds and air turbulence in between, would be “the most difficult sniper shot ever”.

But if the project is successful, further Micius satellites will follow, allowing a global quantum-encrypted network by 2030. Technologies like quantum computing and artificial intelligence are seen as the next big thing in almost every sector, from healthcare to industrial production. In the face of ever more powerful hacking and surveillance - which could one day also include powerful quantum computers - the security of digital communication is increasingly important.

Canada, the US, Japan, the European Space Agency and others are also involved in this field but with much smaller, less risky projects. China has allocated vast amounts of money for basic scientific research in its latest five-year development plan. It's also willing to take big risks on some as-yet unproven technologies.

With ambitious projects, China is ready to reclaim the glory of its past, when inventions like paper, printing, gunpowder and the compass were made. However, China's economic growth is exhausted and there has been a worrying slowdown in private investment in the tech sector. Despite the quantum leap that China is making, there might be hard times ahead for innovation outside big science projects.

Source: BBC

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