http://www.newscientist.com/news/news.jsp?id=ns99991346
Entangled clouds raise hope of teleportation
19:00 26 September 01
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)
19:00 26 September 01
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