Teams of Physicists have Successfully "Teleported" Light-Carrying Particles


Teleporting, the Quantum Way
By James Schultz
Special to

Source: on_001012.html

October 12, 2000

You're under attack in an alien world. You're outgunned, out-manned. It's time for a quick getaway -- it's time to teleport.

Of course, in the fictional Star Trek universe, all you'd have to do is request an "immediate beam-out." In the real world, as scientists currently understand it, your time would be better spent dictating your last will and testament.

On the other hand, if you were a photon... an atom or a molecule, maybe even a single-celled critter... there may be hope.

Spooky science

Building on a landmark paper first published in 1993 that examined methods of applying a phenomenon known as "entanglement," teams of physicists at laboratories in Austria, Italy and the United States have successfully "teleported" light-carrying particles called photons.

Strictly speaking, the teleportation process involves a photon's individual quantum state, a key characteristic that defines that particle's nature and behavior. Teleportation isn't exactly faster-than-light, in the sense that an intermediate, light-speed-or-below step is required.

One technique to create entanglement involves sending a brief pulse of ultraviolet light through a specialized crystal that splits a single, high-energy photon into two lower-energy photons. Because the particles' polarization -- a mathematical property that describes a photon's physical orientation -- is complementary, the photons are said to be entangled.

In order to teleport, however, a third photon must also be involved.

When the first of the two originally entangled photons --- call it photon A --- is sent to the same location as an un-entangled third photon --- call it photon C --- then A and C subsequently become entangled. A special test, known as a Bell-state measurement is then conducted, and photon C loses its original quantum-state identity. Instantly, the second of the two originally entangled photons --- call it photon B --- is itself transformed: B becomes C. For all practical purposes, photon C has teleported to B's location. And B is nowhere to be found.

Despite B's quantum-state destruction (because its polarization is now that of C, for all intents and purposes, B is C and no longer B), no cosmic rules have been broken. No information has been sent faster than light because, for B to become C, information on A's properties must be communicated via light-speed-observing devices like radios, telephones or computers.

Additionally, there is no violation of the Heisenberg uncertainty principle, which holds that no observer can know both the position and speed of a basic particle (which would allow otherwise impermissible, exact copying of matter down to the subatomic level).

Still, the strange fact that one particle can "know" the state of another led Albert Einstein to describe entanglement as "spooky action at a distance" when he and colleagues Boris Podolsky and Nathan Rosen first described entanglement (called by insiders the EPR effect) in the 1930s.

"It's as if two particles are in direct communication with one another regardless of distance," says Williams Wootters, professor of physics at Williams College and a co-author of the 1993 paper that inspired the quantum teleportation experiments. "Entanglement seems to have nothing to do with separation. Teleportation should work no matter how far sender and receiver wander."

Are people next?

Teleporting a photon is one thing, but teleporting people is quite another. A photon has a relatively simple structure. By contrast, human beings are comprised of a mind-boggling array of particles arranged in particular ways.

Not only would scientists need to exploit as-yet-undiscovered means of exactly duplicating the quantum states of all the particles in a human body, but fantastically powerful computers would also be required for accurate reconstitution.

Even given enough raw materials from which to build a teleport object, atom by atom, the time required for reconstruction appears to be so ridiculously long, making any such effort impractical.

"In principle, you can recreate anything anywhere, just as long as you send information on the object luminally, you have the raw materials and you're willing to destroy the original," said Hans Christian von Baeyer, author of Taming The Atom and Chancellor Professor of physics at the College of William and Mary.

"But it would take an unbelievable amount of data processing. Even a coffee cup, without the coffee, would take many times the age of the universe. Right now teleporting the information that comprises a human being seems outrageously impossible."

In his book The Physics of Star Trek, physicist Lawrence Krauss, Professor of Astronomy and chair of the Department of Physics at Case Western Reserve University, describes the difficulties of building a Trek-like transporter as nearly insurmountable.

In some 200 years, assuming continuing improvements to computers, Krauss says we may have the requisite computational power for teleportation. But there will be plenty of other problems that appear to contemporary eyes to be insolvable.

"A single particle like a photon can tunnel through a barrier, disappearing on one side and appearing on the other," Krauss said. "We can't walk through walls. People are a complex, classical system [of particles]. Some day we may figure out ways to make classical systems behave quantum mechanically. But there's a big difference in declaring something possible and then making it practical. Transporting anything other than a particle is extremely implausible."

The future of weird

What may be practical in the short term is the application of quantum-teleportation techniques to information processing and cryptography. In theory, quantum computing would be so fast as to make contemporary supercomputing seem like slow-motion stone carving. And quantum-mechanics-based encryption would, by its very nature, be unbreakable.

"I think we'll be able to exploit quantum weirdness over the next century," Krauss said. "Technology will allow us to see the application of quantum mechanics on ever larger scales. As a result we 'll find devices and uses that people haven't thought of. It'll be new and ingenious and unexpected."

Writing in Scientific American, Austrian physicist Anton Zeilinger takes a bullish view on teleportation's potential, declaring that ways soon many be found to teleport more complex systems without violation of any physical laws. "The entanglement of molecules and then their teleportation may be reasonably be expected within the next decade," he wrote. "What happens beyond is anybody's guess."

Teleportation's ultimate payoff may be an enhanced understanding of quantum mechanics. For physicists, the experimental validation of theory may be satisfaction enough. But for society at large, the benefit from quantum weirdness -- quantum science has thus far led to semiconductors, lasers, CD players and all manner of things digital --- may be substantial and tangible.

"All my career I've heard people say, 'Don't worry about the deeper meaning of quantum mechanics. Just shut up and calculate,'" von Baeyer said. "Now people are digging at the roots. People are talking seriously about actual machines. We'll end up with a far better understanding than we've ever had."

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