Date: Wed, 26 Sep 2001 14:38:22 -0400 (EDT)
From: AIP listserver <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: update.558
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 558 September 26, 2001 by Phillip F. Schewe, Ben Stein,
and James Riordon
ENTANGLEMENT OF MACROSCOPIC OBJECTS, a pair of
gas clouds containing a trillion atoms each, has been achieved by a
research team in Denmark (Eugene Polzik, University of Aarhus,
011-45-89423745, [EMAIL PROTECTED]), constituting by far the
largest material objects entangled on demand and paving the way
for quantum teleportation between macroscopic objects. The
accomplishment, published in this week's issue of Nature
(Julsgaard et al., 27 September 2001), was announced in
preliminary form this June at the first International Conference on
Quantum Information, sponsored in part by the Optical Society of
America and the American Physical Society. One of the most
profound features of quantum mechanics, entanglement is a special
interrelationship between objects in which measuring one object
instantly influences the other, even if the two are completely
isolated from one another. No previous entanglement with atoms
has involved more than four particles. Furthermore, atoms have
only been entangled at close proximity, either as ions spaced
microns apart in a tiny trap (Update 475), or atoms flying over a
short range through narrowly spaced cavities (Hagley et al., Phys.
Rev. Lett., 7 July 1997). In the present experiment, researchers
sent a light beam through two cesium gas samples, each held in a
special paraffin-coated cell. The beam changed each sample's
"collective spin," which describes, in a sense, the net direction in
which all of the atoms' tiny magnets add up. First, the researchers
measured the sum of the two collective spins without knowing the
individual collective spin of each sample. A subsequent
measurement, nearly a millisecond later, showed that the sum
remained the same. This demonstrated that the two gas samples
maintained their special interrelationship and were entangled.
Although the two samples were just millimeters apart, they could
in principle be separated, and thereby entangled, at much longer
distances. Entanglement of such large objects enables "bulk"
properties, like collective spin, to be "teleported," or transferred,
from one gas cloud to another.
THE BLACK HOLE OF GENEVA. Black holes are known as the
omnivorous destroyers of stars. In reality black holes not only take
but give. Near their event horizons, where space is so drastically
warped, black holes spawn particle-antiparticle pairs out of sheer
vacuum. In some cases one of the pair escapes beyond the horizon
while its counterpart is pulled back into the hole. Thus black holes
can shed energy in the form of this "Hawking radiation."
Physicists hope to bring this whole process down to earth by
manufacturing tiny black holes amid the stupendous smashups of
protons at the Large Hadron Collider (LHC) being built at CERN.
Until recently theorists thought gravity was so weak compared to
the other forces that it, and gravitationally bound objects like black
holes, could be studied on an equal footing with the other forces
like the strong nuclear force only at energies of 10^19 GeV. In
the past few years, though, some models featuring extra spatial
dimensions hint that the unification of the forces, including
gravity, might set in at much more modest energies, even in the
TeV realm of the LHC. Thus one can contemplate forming a TeV-
mass black hole even as one can imagine creating new particles in
that mass range. But what would a black hole look like? Savas
Dimopoulous of Stanford (650-723-4231) and Greg Landsberg of
Brown University ([EMAIL PROTECTED], 401-863-1464)
have drawn a picture in which proton-proton collisions could
create black holes with a cross section (likelihood of creation) only
about a factor of ten less than for producing top quarks and at a
rate of up to one per second (see figure at
http://www.aip.org/mgr/png). A black hole produced in this way
would quickly decay, not in the usual particle way but in a furious
burst of Hawking radiation. A particularly striking signature of the
black hole would involve an electron, muon, and photon in the
final state of debris particles. Properties of Hawking radiation
could tell physicists about the shape of extra spatial dimensions. A
possibility of recreating the early moments of the universe in the
lab would further unite particle physics and cosmology (Physical
Review Letters, 15 October 2001; text at
http://www.aip.org/physnews/select)
TURING MODEL FOR LADYBUG BEETLE PATTERNS.
Zebras, leopards, and giraffes are just a few creatures exhibiting
intricate patterns that can be duplicated with models pioneered by
the late mathematical genius Alan Turing (Update 80). The models
are based on diffusion equations, which are often used to describe
the spontaneous mixing of materials over time. As a rule,
mathematicians and physicists have studied Turing models of
biological patterns as though they were formed on flat surfaces. Of
course, few animals tend to be flat, unless they've lingered too long
on a highway. Although Turing models can mimic tiger stripes and
cheetah spots fairly well despite this simplifying assumption, a
group of researchers from the National Chung-Hsing University in
Taiwan decided to consider a slightly more complex shape. When
S.S. Liaw ([EMAIL PROTECTED], 011-8864-2284-0427) and
colleagues studied Turing models on a portion of a spherical
surface, patterns reminiscent of those on lady bug beetles emerged.
There are over 4500 species of lady bugs, most bearing unique,
recognizable designs in contrasting colors such as black and red.
By adjusting coefficients in the model's equations and varying the
initial distributions of hypothetical compounds that mix to create
the colors, the researchers could reproduce the stripes, swirls, and
spots that decorate many of these predatory insects.
The new model shows that an animal's specific geometry is
important in determining it's adornment, and adds weight to
Turing's proposal that diffusion is potentially a mechanism that
helps generate an endless variety of patterns in nature. (S. S. Liaw;
C. W. Yang; R. T. Liu; J. T. Hong, Physical Review E, October
2001; text at http://www.aip.org/physnews/select)
