Quantum communication in China

Schroedinger's cat is relaying messages on the Great Wall of China.

Jian-Wei Pan of the University of Science and Technology of China in Hefei and his colleagues successfully transmitted "entangled" photons through more than 7 kilometres of the Earth's turbulent lower atmosphere without losing the photons' fragile quantum properties.

Quantum entanglement is a way of merging the quantum mechanical properties of two particles. If you can avoid observing them right away, you can pull interesting behavior out of the system.

Quantum entanglement allows two particles to behave as one even if they are very far apart. Measure the property of one particle and you instantly know the property of the other. Entanglement allows you to transmit secure encryption keys over a public channel, but until now the furthest anyone had transmitted entangled particles through air was about 600 metres. <snip> Depending on atmospheric conditions, the amount of air between a base station and a satellite in low Earth orbit is equivalent to 5 to 10 kilometres of air at ground level, so the Chinese experiment brings satellite-based quantum communication within reach.

This means the system can now be used in secure satellite communications.