PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 626 February 26, 2003   by Phillip F. Schewe, Ben Stein, and James
Riordon

3600 ATOMS IN TWO PLACES AT ONCE.  Bose Einstein condensates (BEC), clouds
of ultracold atoms which fall together into a single coherent state,
continue to be a marvelous working material for studying subtle quantum
effects.  Last year physicists at the Max Planck Institute for Quantum
Optics (MPQ) managed to load a BEC of rubidium atoms into a
three-dimensional optical lattice, an artificial crystalline environment in
which crossing laser beams provide the forces needed to pinion atoms in the
3D equivalent of an egg crate.  Moreover, by a delicate modification of the
laser light the resident atoms could be made to undergo a quantum transition
between two phases.  In one phase the atoms constitute a superfluid: all the
atoms have a coordinated wave function, but the number of atoms in any one
"well" in the egg carton is unknown.  In the other phase the atoms
constitute an insulator: the number of atoms in each well is known exactly
to be equal to one, but the atoms are all uncoordinated with respect to each
other (that is, they no longer can be considered a coherent quantum
material).  These were the results as of a year ago (see Greiner et al.,
Nature, 3 January 2003.)  Speaking at last week's meeting of the American
Association for the Advancement of Science (AAAS) in Denver, Immanuel Bloch
reported that he and his MPQ colleagues have exploited the fact that the Rb
atoms possess two magnetic substates and have succeeded, by a further
adjustment of the confining laser beams, to separate each atom into two
entangled spatially separated  parts.  The researchers are also attempting
to get the different diploid atoms (an average of 3600 per plane in the
lattice) to interact; one aim is to engineer an unprecedented degree of
quantum entanglement, possibly for computational purposes.

TUNABLE OPTICAL FIBERS.  Optical fibers regularly carry billions of phone
conversations and other data transmissions every day and are a fundamental
part of optical sensing and numerous medical applications.  The photonic
devices responsible for all this traffic are being made even more efficient
and versatile by handing over some of the switching and reconfiguring chores
to the fibers themselves---the trunk lines linking all the optical nodes. An
active optical fiber, which can tunably filter light at different
frequencies, has been created by infusing microfluidic plugs, spaced at
characteristic (periodic) intervals along the fiber, into air holes running
parallel to the passageway for the light at the center of the fiber (see
figure at http://www.aip.org/mgr/png/2003/180.htm ).  The arrays of
microfluidic plugs along the light path serves as a diffraction grating for
producing the photonic-crystal effect.  In other words, the presence of the
fluids is used to change the refractive index periodically, and hence the
transmission properties, of the fiber.  The creators of this new
microstructured optical fiber (MOF), Charles Kerbage (OFS Laboratories in
Murray Hill, NJ; kerbage{at}ofsoptics.com) and Ben Eggleton (University of
Sydney, egg{at}physics.usyd.edu.au), say that this is the first time a tunable
grating has been achieved with microfluids, and that this provides (in
addition to the switchability) a very high index of refraction when compared
to conventional gratings. (Applied Physics Letters, 3 March 2003)

SHAKEN NOT STIRRED. The progression toward smaller and smaller electrical
and mechanical components presents tremendous challenges to engineers and
scientists as they strive to create devices on scales measured in microns
and nanometers. One solution may be to develop materials that automatically
arrange themselves in useful patterns. Now a collaboration of researchers
(Igor Aronson, aronson{at}msd.anl.gov, 630-252-9725) at Argonne National
Laboratory and Institute of Physics for Microstructures of the Russian
Academy of Sciences has developed a new method for encouraging microscopic
particles to self assemble into desired complex patterns. The technique is
inspired by the patterns formed in shaken mixtures of much larger granular
materials.
Numerous, beautiful experiments involving agitated containers of sand, ball
bearings, or other granular materials have shown that the combination of
gravity and inter-particle forces from collisions can lead to a rich variety
of patterns, ranging from particle-like localized excitations known as
oscillons to honeycomb shapes to chaotic swirls (Update 264). Other studies
have helped to explain why large and heavy brazil nuts sometimes rise to the
top in shaken containers of mixed nuts (Update 132).  The new research
extends such experiments into microscopic regimes.
Rather than mechanically agitating tiny grains to create self assembled
patterns, however, the method relies on electrostatic fields to drive
metallic microparticles immersed in liquids. The researchers placed
120-micron bronze spheres in a mixture of toluene and ethanol trapped
between glass plates. The plates were coated with thin layers of transparent
conducting material, and an electric field of up to 3 kilovolts per
millimeter was applied between them. Particles that contacted the lower
plate acquired a charge and were repelled toward the upper plate. If the
upward electrostatic force is sufficient to overcome gravity, the particles
fly upward, contact the upper plate where their charge is reversed, and then
are forced back down again. In effect, the alternating charge on the
particles is analogous to shaking a container of macroscopic grains. As in
the classic granular material experiments, varying the conditions causes the
particles to form vortices, pulsating rings, honeycomb patterns, or other
structures (see figure at www.aip.org/mgr/png ). Ultimately, say the
researchers, studies such as this may allow us to design systems that
spontaneously self assemble into useful structures on increasingly tiny
scales. (M. V. Sapozhnikov, Physical Review Letters, upcoming article)

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PHYSICS NEWS UPDATE is a digest of physics news items arising
from physics meetings, physics journals, newspapers and
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