Wireless Transmission of Quantum Code

Wireless transmission of quantum code over a distance of 144 kilometers (89 miles) between two Canary Islands has been demonstrated by a team of researchers in Europe. At the APS March Meeting, Anton Zeilinger of the University of Vienna (anton.zeilinger@univie.ac.at) described how he and his colleagues transmitted single photons from an astronomical observatory in La Palma Island to another one in Tenerife.

The transmitted photons' polarization states (representing 0s and 1s) formed the basis of a "quantum key," a stream of information that could be used to decipher a longer encrypted message. The researchers used single photons because they are more secure than groups of photons, from which an eavesdropper could pluck information about the key.

To detect potential eavesdroppers even better, the researchers entangled the outgoing particles of light with photons kept at the transmitting station. They used astronomy stations because their telescopes are sensitive enough to detect individual photons. The data transmission rate was low, only 178 photons in 75 seconds, but the photons are able to travel longer distances in free space (potentially thousands of kilometers or more) than they are in fiber optic cables (100 km) before they become undetectable.

In a proposed experiment to be coordinated by the European Space Agency (ESA, which operates the Tenerife telescope and which participated in the Canary Islands experiment) the International Space Station can transmit entangled key to two earthbound stations separated by distances ten times greater or more. (For a preprint, see Ursin et al., quant-ph/0607182)