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Quantum Satellite Micius Challenges Einstein

Quantum Satellite Micius Challenges Einstein

By Paul Edwards

Quantum cryptography experiments onboard a new Chinese Earth satellite foreshadow secret communications on a global scale with security guaranteed by the laws of physics.

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Albert Einstein was never happy with the more bizarre predictions of the quantum theory that he had pioneered. In particular he was worried about what he called “spooky action at a distance” – the prediction that a measurement made at a remote location, no matter how distant, could instantaneously change the results of a local measurement. He realised this quantum entanglement violated the concept of a deterministic universe having an independent reality in which the speed of light limited the propagation of all physical effects through space.

Nevertheless, following the work of Irish physicist John Bell, Einstein’s spooky action at a distance has been demonstrated and confirmed by increasingly rigorous experiments up to distances of hundreds of kilometres. With the launch of the Chinese earth satellite Micius in August last year into a Sun-synchronous low-Earth orbit 500 km high, the bizarre property of quantum-entangled pairs of light photons is now being tested in space as a means of implementing secret worldwide communication.

Micius represents a major advance in the field of quantum cryptography, aiming to extend the secure distribution of private quantum keys to global distances for the first time. It is the culmination of several decades of international research, including early Australian work on the feasibility of quantum cryptography with LEO...

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