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"Beam Me Up"

An experiment confirms that teleportation is possible--at least for photons
Captain Kirk and his crew do it all the time with the greatest of ease: they discorporate at one point and reappear at another. But this form of travel long has seemed remote to the realm of possibility. Now, however, it turns out that in the strange world of quantum physics, teleportation is not only theoretically possible, it can actually happen.
Zeilinger
Image: University of Innsbruck
ANTON ZEILINGER and his coworkers designed the first experiment to verify quantum teleportation.

One group of researchers at the University of Innsbruck in Austria published an account of the first experiment to verify quantum teleportation in the December 11 issue of Nature. And another team headed by Francesco De Martini in Rome has submitted similar evidence to Physical Review Letters for publication. Neither group sent a colleague to Katmandu or a car to the moon. Yet what they did prove is still pretty startling. Anton Zeilinger, De Martini and their colleagues demonstrated independently that it is possible to transfer the properties of one quantum particle (such as a photon) to another--even if the two are at opposite ends of the galaxy.

Until recently, physicists had all but ruled out teleportation, in essence because all particles behave simultaneously like particles and like waves. The trick was this: they presumed that to produce an exact duplicate of any one particle, you would first have to determine both its particlelike properties, such as its position, and its wavelike properties, such as its momentum. And yet doing so would violate the Heisenberg uncertainty principle of quantum mechanics. Under that principle, it is impossible to ever measure wave and particle properties at the same time. The more you learn about one set of characteristics, the less you can say about the other with any real certainty.

Bennett
Image: Andre Berthiaume

IBM CREW Six researchers--Richard Jozsa, William K. Woolters, Charles H. Bennett (back row, left to right) Gilles Brassard, Claude Crepeau and Asher Peres (front row)--proposed quantum teleportation in 1993.

In 1993, though, an international team of six scientists proposed a way to make an end-run around the uncertainty principle. Their solution was based on a theorem of quantum mechanics dating to the 1930s called the Einstein-Podolsky-Rosen effect. It states that when two particles come into contact with one another, they can become "entangled." In an entangled state, both particles remain part of the same quantum system so that whatever you do to one of them affects the other one in a predictable, domino-like fashion. Thus, the group showed how, in principle, entangled particles might serve as "transporters" of sorts. By introducing a third "message" particle to one of the entangled particles, one could transfer its properties to the other one, without ever measuring those properties.

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EXPERIMENTAL PROOF

Bennett's ideas were not verified experimentally until the Innsbruck investigators performed their recent experiment. The researchers produced pairs of entangled photons and showed they could transfer the polarization state from one photon to another.

Teleportation still has one glitch: In the fuzzy realm of quantum mechanics, the result of the transfer is influenced by the receiver's observation of it. (As soon as you look at, say, Bones, he will look like something else.) So someone still has to tell the receiver that the transformation has been made so that they can correctly interpret what they see. And this sort of communication cannot occur at faster-than-light speeds. Even so, the scheme has definite applications in ultrafast quantum computers and in utilizing quantum phenomena to ensure secure data transmission [see QUANTUM CRYPTOGRAPHY, Charles H. Bennett, Scientific American, October 1992].

For now, though, it will be a long time before a real Scotty beams up a living Captain Kirk.

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