From: LARRY KLAES (ljk4@msn.com)
Date: Sun May 12 2002 - 13:52:49 PDT
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From: AIP listserver
Sent: Saturday, May 11, 2002 9:15 PM
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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 588 May 9, 2002 by Phillip F. Schewe, Ben Stein, and
James Riordon
BRIGHT SOLITONS IN A BOSE-EINSTEIN CONDENSATE
have been created and observed for the first time by a Rice
University team (Randy Hulet, 713-348-6087,
randy@atomcool.rice.edu), yielding a stunning new demonstration
of the wavelike behavior of atoms and providing an important tool
for eventual technological applications of BECs. First observed on
the surface of a narrow canal in 1834, a soliton is a group of waves
combining in such a way to form a single composite wave that can
travel for long distances without spreading out or losing its original
shape. Solitons can occur in all kinds of waves; for example, they
have been thoroughly studied in sound waves and light waves. In
fact, soliton light waves are currently employed in
telecommunications. Solitons can exist in BECs too. Since a BEC
consists of ultracold atoms all in the same quantum state, it
exhibits wavelike behavior and therefore can be considered as a
single atom wave. However, the BEC atom wave usually spreads
apart or "disperses" shortly after the BEC is released from a trap.
Nonetheless, in previous BEC experiments (such as Burger et al.,
Phys. Rev. Lett., 20 December 1999), researchers have observed
"dark solitons," representing absences of atoms that can propagate
without changing shape in a condensate. Now, in a BEC of
lithium atoms, the Rice team has produced "bright" solitons, each
representing a condensate of actual atoms extracted from the main
BEC. In effect, the bright solitons are individual atom waves
broken off from the main BEC atom wave. Using a narrow laser
beam to guide BEC atoms in a single-file line, the Rice team
tailored the interactions between lithium atoms to be attractive so
that the atoms' attraction for one another perfectly offset their
predisposition to spread out. With their technique, the Rice
researchers have created "trains" of up to 15 solitons (see figure at
www.aip.org/mgr/png). These atom-wave solitons will likely be a
useful tool someday for BEC versions of gyroscopes for ultra-
precise navigation and very accurate atomic clocks (Strecker et al.,
Nature, 9 May 2002 print issue; this work will also be presented in
papers G1.011 and R1.001 at the upcoming APS Division of
Atomic, Molecular, and Optical Physics (DAMOP) meeting in
Williamsburg from May 29-June 1.)
ANOTHER UNIVERSE MIGHT LURK ONLY MILLIMETERS
away from our universe, but we wouldn't know it because it exists
on its own membrane separated from our membrane in some extra
spatial dimension. Matter on the other membrane would be
invisible but could exert a gravitational effect and would, in fact,
constitute the "dark matter" for which astrophysicists have sought
for some years. In a recent paper Paul Steinhardt (Princeton) and
Neil Turok (Cambridge) propose that the structure in our universe
may well have come about in the collision of two such membrane
universes. All the historical events in the life of our
cosmos initial big bang, subsequent expansion of galaxies, even
the currently observed accelerated expansion phase, and finally a
contraction into a "big crunch" would be played out in a recurring
drama. This cyclic cosmology (an extension of Steinhardt's
"ekpyrosis" theory; see Update 535) uses all the latest tools of
string theory, accounts for the "dark energy" supposedly firing
cosmic acceleration, and would have no need for an ad-hoc
"inflationary" phase appended to the standard big bang model to
explain such cosmological features such as the horizon problem
(why the extreme edges of the visible universe seem to be at the
same temperature). (Sciencexpress, 25 April, soon to be in
Science.)
TUNGSTEN PHOTONIC CRYSTAL. Shawn Lin and his
colleagues at Sandia have made a photonic crystal, a lattice of
atoms that excludes light at certain wavelengths, out of tungsten.
They did this creating a special semiconductor structure with
conventional lithographic methods, then removing selectively
some of the material and backfilling with a vapor of tungsten.
Metal photonic crystals have been made before but the Sandia
model is the first to operate (exclude light) over the range of 8 to
20 microns. By excluding light in this stretch of the infrared a
lightbulb filament fashioned into a photonic crystal geometry
might be much more efficient than existing versions by redirecting
more energy into producing light rather than heat. (Fleming et al.,
Nature, 2 May 2002.)
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