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Physicists Teleport Quantum Bits Over Long Distance

By John Roach
for National Geographic News
January 29, 2003
 
Fans of the television and movie series Star Trek often lust after the technology that allows characters to step onto a transporter and be instantaneously whisked from one room on the U.S.S. Enterprise to another room, another planet, or another universe.

The technology is known as teleportation. It involves taking away the material properties of an object at one location and transferring the exact details of its configuration to another location where it is reconstructed.

Today, scientists debate whether human teleportation as depicted by the Star Trek series is theoretically possible or even desirable, but over the last decade they have made great strides in the field of quantum teleportation.



Quantum teleportation is the transferring of tiny units of computer information, called quantum bits or qubits, from one location to another. The technology is referred to as a type of teleportation because the information teleported behaves more like an object than normal information.

"It is quantum information, which cannot be copied and cannot appear at the new location without being destroyed at the old location," said William Wootters, a physicist at Williams College in Williamstown, Massachusetts who co-authored a 1993 paper that outlined the theory of quantum teleportation.

Scientists treat quantum information as if it were an object. The fact that the information cannot be conveyed without first being destroyed also differentiates quantum teleportation from faxing a document, which makes an imprecise replica of the original at another location and leaves the original intact.

Since Wootters and colleagues published their paper in 1993, scientists have worked to prove the theory correct. The most recent success is reported by a team of physicists from the University of Geneva in Switzerland in the January 30 issue of Nature.

"We report the first experimental long distance demonstration of this fascinating aspect of quantum mechanics," said Nicolas Gisin, a physicist at the University of Geneva.

His team teleported qubits carried by photons—particles of light—of 0.05 inch (1.3mm) wavelength in one laboratory onto photons of 0.06 inch (1.55mm) wavelength in another laboratory 180 feet (55 meters) away along 1.2 miles (2 kilometers) of fiber optic wire.

In 1997 and again in 1998, scientists successfully demonstrated the concept of quantum teleportation by transferring two dimensional systems over short distances, such as from one side of a table to the next. Gisin and his team prove that the concept of quantum teleportation holds up at longer distances.

"Gisin's work sounds like a significant achievement," said Samuel Braunstein, a professor of informatics at the University of Wales in Bangor, England who was part of a team that teleported photons from one end of a table to the next in 1998.

Entanglement

Until 1993, scientists considered teleportation impossible because it requires making an exact copy of every atom in an object, which goes against the so-called uncertainty principle of quantum mechanics. According to the principle, the very act of measuring a tiny particle destroys it, so an exact replica can never be made.

Wootters and his colleagues showed that the way around the problem is to rely on the concept of entanglement, an area of physics that Albert Einstein referred to as "spooky action at a distance."

"If two particles are entangled, they act in some respects as if they were a single object," said Wootters. Everything that happens to one of the entangled pairs instantly affects the other, no matter how far apart each of the entangled particles is from the other.

Braunstein likens entanglement to "a pair of ideal lovers who know each other so well that they could answer for their lover even if separated by long distances."

Entangled pairs are made by taking one photon and converting it into a pair that fly off in opposite directions. By imposing the object to be teleported on one member of the entangled pair, the object is instantaneously imposed on the other member of the entangled pair.

That, say the scientists, is quantum teleportation, even though a precise measurement of the object teleported was never made.

Applications

Scientists believe that this technology has practical applications in the field of quantum computing and quantum cryptology, technologies that hold promises for making computing both much faster and secure.

"The possible applications concern communication between future quantum computers and also between gates inside an individual quantum computer," said Anton Zeilinger, a physicist at the University Vienna in Austria who was part of the team that achieved quantum teleportation in 1997.

Wootters explained that the technology could allow computers to send the code to unlock secret messages between each without the fear of another computer intercepting the code or the code deteriorating as it traveled over conventional communications mediums such as a fiber optic wire.

However, Star Trek fans probably have a long wait ahead of them before they will be able to step onto a transporter and be whisked instantaneously to their desired location.

"With today's technology, only very elementary objects can be teleported," said Gisin. "Possibly, larger objects like a molecule will be teleported in my life-time, but really large objects are not teleportable using foreseeable technologies."

Scientists say there is simply too much information in a human that needs to be teleported to make this technology applicable.

"The key thing for now is the sheer amount of information involved," said Braunstein. "Even with the best communication channels we could conceive of at the moment transferring all that info would take the age of the universe."
 

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