Friday, March 09, 2007

Spooky quantum link - photons fly far

The reach of the spooky quantum link called entanglement keeps getting longer. A team has transmitted entangled photons some 144 kilometers (89 miles), reports Scientific American.

The distance achieved is 10 times farther than entangled photons have ever flown through the air. When two photons or other particles are in this state, what happens to one determines the fate of the other, no matter how far apart they are. Physicist Anton Zeilinger compares the phenomenon with throwing a pair of dice that land on matching numbers every time.

Using a laser, the researchers created entangled pairs of photons on La Palma and fired one member of each pair to a European Space Agency (ESA) telescope on Tenerife, which had to make rapid, small adjustments to receive the photons, Zeilinger says. In another presentation, physicist Richard Hughes of Los Alamos National Laboratory described recent experiments in which his group fired a series of nonentangled photons 185 kilometers down a conventional optical fiber.

In both cases, researchers demonstrated that they could transmit randomly oriented, or polarized, photons, which are suitable for sending messages that cannot be intercepted without garbling the information. Called quantum keys, such transmissions could allow users to scramble messages in a way that is potentially unbreakable.