Photons teleported six kilometers

April 21/28, 2004

Real-life teleportation will never come close to the teleportation of fiction, but instantly sending single quantum particles like photons from one place to another has been proved possible in laboratory experiments.

The ability promises to extend the reach of quantum cryptography, which offers potentially perfect security.

Researchers from the University of Geneva have moved quantum teleportation a step forward by instantly transporting qubits -- photons whose properties can represent a 1 or a 0 -- over six kilometers of optical fiber.

The light pulses that transport information over today's long distance optical fibers are each made up of billions of photons and the signals are able to travel long distances only because the pulses are periodically refreshed.

Quantum cryptography signals cannot be refreshed because copying them destroys the information they carry. Teleportation is akin to a fax machine for quantum particles. A pair of photons are entangled, or linked so that their properties remain in lockstep, and one of the pair is sent to the receiver. The particle to be transported is brought into contact with the sender's half of the pair, which destroys the original particle but in the process turns the receiver's half of the pair into an exact replica.

The quantum relay could span several hundred kilometers. Longer distances would require quantum repeaters, which require quantum memory. Researchers are still figuring out how to make quantum memory.

It is too soon to say when quantum relays could be used practically, according to the researchers. The work appeared in the January 29, 2004 issue of Physical Review Letters.

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