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CLOUDS of trillions of atoms have for the first time been linked by quantum
鈥渆ntanglement鈥濃�攖hat 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, and can be persuaded to interact with each other so that events
affecting one instantly affect another鈥攏o 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.

The team coordinated the quantum states of two atom clouds by exploiting a
loophole in Heisenberg鈥檚 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鈥攁eons by quantum
standards.

鈥淭he experiment shows that it is possible to create entanglement with
macroscopic objects, and to do it using just laser light鈥攚hich means one
can do it even when the objects are separated by substantial distances,鈥� says
the team leader, Eugene Polzik. 鈥淲e鈥檝e also shown that the state can persist for
a long time, even at room temperature.鈥�

鈥淣ow 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,鈥�
says Ignacio Cirac, a physicist at the University of Innsbruck in Austria.
Advances could lead to real-life quantum communication systems, teleportation
and quantum computers.