China's quantum satellite sends unbreakable signals from space


Bolstered by the success of its first quantum communications satellite, China is eyeing the next steps in a quest to make a secure global network. Quantum networks are also theorized to be hack-proof because observing the keys that are used to unlock the data would destroy them due to their quantum nature. This satellite, weighing more than 600 kg, is now orbiting the Earth at an altitude of 500 kilometers.

For a crack group of Chinese scientists, "hack-proof" communications have quickly become a reality - using what is commonly known as "quantum key distribution" to help revolutionise how secure messages are sent across the globe, using satellite-to-ground technology. This is the first ever code of its own nature.

Pan Jianwei, an academician at state-run Chinese Academy of Sciences and the lead scientist of Quantum Experiments at Space Scale (QUESS) Experiment says quantum teleportation technology allows transfer of unknown quantum states from one object to another over a long distance.

( Chinese teams working with quantum encryption and entanglement have achieved two more goals toward building a quantum space-based communication network.

Long-distance teleportation is considered a fundamental element in protocols involving distributed quantum computation and large-scale quantum networks.

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The first experimental verification of quantum teleportation was carried out in 1997 by Austrian quantum physicist Anton Zeilinger. A solution, however, lies in exploiting space-based links that could greatly reduce channel loss while establishing a communication between two remote places on Earth.

To solve the issue, satellites will soon be sent into higher orbit, with scientists teasing the creation of a so-called "satellite constellation".

"If we have a satellite in orbit at 10,000km, the time for quantum key distribution could be several hours", Peng noted.

The communication distance between the satellite and the ground station varies from 645 kilometres to 1,200 kilometres, and the quantum key transmission rate from satellite to the ground is up to 20 orders of magnitude more efficient than that expected using an optical fibre of the same length, said Pan.

And, any attempt to eavesdrop on the quantum channel would introduce detectable disturbances to the system, "Once intercepted or measured, the quantum state of the key will change, and the information being intercepted will self-destruct", added Pan.