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China launches quantum satellite to test spooky action at a distance

Entangled photons will also be used for encryption key exchange … in Spaaaaaaace

By Simon Sharwood, 16 Aug 2016

China has launched a satellite dubbed “Micius” that bears the Quantum Experiments at Space Scale (QUESS) instrument it will use to test quantum communications between Earth and space.

QUESS' key payload is entangled photons. A quick primer: if you fire a photon at certain crystals it will split into two photons. Both of those photons will have exactly the same qualities. Almost miraculously, any change to the first photon will be mirrored in the second. Just how that change propagates across space and time is not understood. It's also thought that whatever it is that lets entangled photons share information may take place faster than the speed of light.

Einstein himself described this as “spooky action at a distance ('pukhafte Fernwirkung').”

We can test this stuff on Earth, but it will be very interesting indeed to see how it goes once we can test it over 500km, the altitude at which Micius will orbit Earth.

China being China, there's a strategic angle to go with the science. The strategic angle is that it's felt whatever channel it is that carries information between photons is utterly unobservable. If one can code an encryption key carried by changes of a photon's state, it should therefore be possible to share that key without possibility of eavesdropping.

China's therefore set up a pair of ground stations that will get keys from Micius and exchange information.

Those tests will doubtless be a success, just like China's moon rover that conked out after a couple of days was judged a success. Hopefully some peer-reviewed papers emerge after the two-year experiment so we can learn more about quantum communications than their undoubted propaganda value. ®

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