[ExI] pop quantum news
thespike at satx.rr.com
Fri Jan 23 05:22:25 UTC 2009
Friday, 23 January 2009
by Jacqui Hayes
SYDNEY: Quantum information has been successfully
teleported between two single atoms a metre apart
a significant step towards long distance
quantum communication and quantum computing, researchers say.
Quantum information is information about the
physical state of a particle: its energy or spin,
for example. Physicists in the U.S. have now
managed to faithfully transfer this information
between two atoms separated by a short distance,
according to their study published today in the journal Science.
"The teleportation of quantum information in this
way could form the basis of a new type of quantum
internet that could outperform any conventional
type of classical network for certain tasks,"
said Christopher Monroe, study author with the
Joint Quantum Institute at the University of Maryland in College Park.
Before now, quantum teleportation had been
achieved over very long distances with groups of
atoms or with photons (see,
communication breaks distance record), but this
is the first time it has demonstrated with single atoms.
Only quantum teleportation between single atoms
is a feasible way to hold and manage quantum
information over long distances. "Photons are
ideal for transferring information fast over long
distances, whereas atoms offer a valuable medium
for long-lived quantum memory," said Monroe.
In the study, the researchers put two ytterbium
ions (A and B) in separate vacuum traps separated
by one metre. Ion A was irradiated by microwaves,
putting it into an unknown quantum state this
state was the information to be transported.
The ions were excited by a laser pulse, which
caused them to emit a single photon and returned
to their initial state. The photons were measured
in such a way that it was impossible to tell
which ion emitted which photon. In the curious
world of quantum mechanics, this projects an
'entangled' state onto the ions....
Once the two ions were entangled, the researchers
took a measurement of ion A. Because ion A and
ion B were entangled, this forced ion B to embody
the initial unknown quantum state of ion A. The
team then applied a microwave pulse to ion B to
recover the original state of ion A.
The researchers report that atom-to-atom
teleported information can be recovered
accurately 90 per cent of the time a figure they hope to improve.
Monroe said that their set-up could one day have
a use as a 'quantum repeater' these tackle the
problem of generating a signal by temporarily
storing the state of a photon. New photons with
the same state are generated at each repeater propagating the signal.
"Our system has the potential to form the basis
for a lage-scale 'quantum repeater' that can
network quantum memories over vast distances,"
added Monroe. Without quantum repeaters,
long-distance quantum communication would not be possible.
"This experiment is an important step toward the
realisation of quantum repeaters," wrote
physicists M. S. Kim and Jaeyoon Cho of Queen's
University in Belfast in an accompanying
commentary in the same issue of Science. "With
the recent experimental advances, the
theoretically presumed quantum paradoxes are
slowly revolutionising information technology."
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