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
(email@example.com) 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