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Harvard University physicists have, for the first time, stopped and
extinguished a light pulse in one part of space and then revived it in a
completely separate location. They accomplished this feat by completely
converting the light pulse into matter that travels between the two locations
and is subsequently changed back to light.
Matter, unlike light, can easily be manipulated, and the experiments provide
a powerful means to control optical information. The findings, published this
week by Harvard University researchers in the journal Nature, could present an
entirely new way for scientists and engineers to manipulate the light pulses
used in fiber-optic communications.
“We demonstrate that we can stop a light pulse in a super cooled sodium
cloud, store the data contained within it, and totally extinguish it, only to
reincarnate the pulse in another cloud two-tenths of a millimeter away,” said
Lene Vestergaard Hau, Mallinckrodt Professor- Physics and Applied
Physics-Faculty of Arts and Sciences and School of Engineering and Applied
Sciences, Harvard.
Hau and her co-authors-Naomi S Ginsberg and Sean R Garner, found that the
light pulse can be revived, and its information can be transferred between the
two clouds of sodium atoms by converting the original optical pulse into a
traveling matter wave, which is an exact matter copy of the original pulse,
traveling at a leisurely 200m per hour. The matter pulse is readily converted
back into light when it enters the second supercooled clouds-known as
Bose-Einstein condensates-and is illuminated with a control laser.
“The Bose-Einstein condensates are very important to this work because
within these clouds atoms become phase-locked, losing their individuality and
independence,” Hau said. “The lock-step nature of atoms in a Bose-Einstein
condensate make it possible for the information in the initial light pulse to be
replicated exactly within the second cloud of sodium atoms, where the atoms
collaborate to revive the light pulse,” he added.
Within a Bose-Einstein condensate, a cloud of sodium atoms cooled to just
billionths of a degree above absolute zero, a light pulse is spatially
compressed by a factor of 50 million. The light drives a controllable number of
the condensate's roughly 1.8 million sodium atoms to enter into quantum
superposition states with a lower-energy component that stays put and a
higher-energy component that travels between the two Bose-Einstein condensates.
The amplitude and phase of the light pulse stopped and extinguished in the first
cloud are imprinted in this traveling component and transferred to the second
cloud, where the recaptured information can recreate the original light pulse.
The period of time when the light pulse becomes matter, and the matter pulse
is isolated in space between the condensate clouds, could offer scientists
and engineers a tantalizing new window for controlling and manipulating optical
information; researchers cannot now readily control optical information during
its journey, except to amplify the signal to avoid fading. The new work by Hau
and her colleagues mark the first successful manipulation of coherent optical
information.
“This work could provide a missing link in the control of optical
information,” Hau said. “While the matter is traveling between the two
Bose-Einstein condensates, we can trap it, potentially for minutes, and reshape
it, change it, in whatever way we want. This novel form of quantum control could
also have applications in the developing fields of quantum information
processing and quantum cryptography.”
Ginsberg, Garner, and Hau's work was supported by the Air Force Office of
Sponsored Research, the National Science Foundation, and the
National Aeronautics and Space Administration.
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