Future Energy eNews Feb. 8, 2002

Two articles from different peer-reviewed journals.


1) Teleporting larger objects becomes real possibility


06 February 02, New Scientist

Anil Ananthaswamy


The dream of teleporting atoms and molecules - and maybe even larger objects - has become a real possibility for the first time. The advance is thanks to physicists who have suggested a method that in theory could be used to "entangle" absolutely any kind of particle.

Quantum entanglement is the bizarre property that allows two particles to behave as one, no matter how far apart they are. If you measure the state of one particle, you instantly determine the state of the other. This could one day allow us to teleport objects by transferring their properties instantly from one place to another.

Until now, physicists have only been able to entangle photons, electrons and atoms, using different methods in each case. For instance, atoms are entangled by forcing them to interact inside an optical trap, while photons are made to interact with a crystal.

"These schemes are very specific," says Sougato Bose of the University of Oxford. But Bose and Dipankar Home, of the Bose Institute in Calcutta, have now demonstrated a single mechanism that could be used to entangle any particles, even atoms or large molecules.

Beam splitter

To see how it works, consider the angular momentum or "spin" of an electron. To entangle the spins of two electrons, you first need to make sure they're identical in all respects but their spin. Then you shoot the electrons simultaneously into a beam splitter.

This device "splits" each electron into a quantum state called a superposition, which gives it an equal probability of travelling down either of two paths. Only when you try to detect the electron do you know which path it took. If you split two electrons simultaneously, both paths could have one electron each (which will happen half of the time) or either path could have both.

Bose and Home show mathematically that whenever one electron is detected in each path, they will be entangled. While a similar effect has been demonstrated before for photons, the photons used were already entangled in another way, even before they reached the beam splitter.

"One of the advances we have made is that these two particles could be from completely independent sources," says Bose.

Massive particles

The technique should work for any objects - atoms, molecules and who knows what else - as long as you can split the beam into a quantum superposition.

Anton Zeilinger, a quantum physicist at the University of Vienna in Austria, has already shown that this quantum state is possible with buckyballs - football-shaped molecules of C60. Although entangling such large objects is beyond our technical abilities at the moment, this is the first technique that might one day make it possible.

Any scheme that expands the range of particles that can be entangled is important, says Zeilinger. Entangling massive particles would mean they could then be used for quantum cryptography, computing and even teleportation.

"It would be fascinating," he says. "The possibility that you can teleport not just quantum states of photons, but also of more massive particles, that in itself is an interesting goal."

Journal reference: Physical Review Letters (vol 88, article 05401), New Scientist (6 February 02)




2) Entangled clouds raise hope of teleportation


26 September 01, New Scientist

Robert Matthews


Clouds of trillions of atoms have for the first time been linked by quantum "entanglement" - that spooky, almost telepathic link between distant particles. The feat opens new possibilities for quantum communication systems and sci-fi-style teleporting of objects from one place to another.

The everyday view of atoms is of solid, independent objects a bit like billiard balls. But according to quantum theory, atoms are far less concrete entities.

Atoms can be persuaded to interact with each other so that events affecting one instantly affect another - no matter how far apart they are. Dubbed entanglement, this could open the way to superfast quantum communications systems and ways of teleporting objects by instantly transferring their properties from place to place.

Before now scientists only managed to entangle a few atoms close together, raising a question mark over the practicality of quantum technology. But now a team at the University of Aarhus in Denmark has entangled two clouds of trillions of caesium atoms. The method should work for very distant clouds.

Quantum loophole

The team co-ordinated the quantum states of two atom clouds by exploiting a loophole in Heisenberg's uncertainty principle. The principle forbids precise knowledge of the quantum state of each gas cloud.

But when two clouds are in an entangled state, you can work out the overall properties of the two collections, for example, the so-called total spin state. Changes in one cloud are mirrored by changes in the other that keep the overall property of both clouds constant.

To preserve the frail entanglement, the team shielded the atom clouds from outside disturbances. They did this using special magnetic fields to trap the atoms inside two vessels lined with paraffin wax.

By shining laser light through the vessels, the team entangled the spin states of the two atom clouds then watched how long the state lasted. Full entanglement would have lasted only a million-billionth of a second, but the team kept up partial entanglement for half a millisecond - aeons by quantum standards.

"The experiment shows that it is possible to create entanglement with macroscopic objects, and to do it using just laser light - which means one can do it even when the objects are separated by substantial distances," says the team leader, Eugene Polzik. "We've also shown that the state can persist for a long time, even at room temperature."

"Now that the experiment has been done, it should be relatively simple to entangle more than two atomic samples, or to teleport states of atomic samples," says Ignacio Cirac, a physicist at the University of Innsbruck in Austria.

Journal reference: Nature (vol 413, p 400), New Scientist (26 September 01)





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