PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 613  November 13, 2002   by Phillip F. Schewe, Ben Stein, and James
Riordon

A BI-PHOTON DE BROGLIE WAVELENGTH has been directly measured in an
interference experiment for the first time.  In the early days of quantum
mechanics, Louis de Broglie argued that if waves could act like particles
(photoelectric effect) then why couldn't particles act like waves?  They
could, as was borne out in numerous experiments (the double-slit experiment
for electrons was voted the "most beautiful" experiment in a
recent poll-see
Physics World, Sept 2002).  In fact intact atoms in motion and even
molecules can be thought of as "de Broglie waves." Molecules as large as
buckyballs (carbon-60) have been sent through an interferometer, creating a
characteristic interference pattern (see Update 579,
www.aip.org/enews/physnews/2002/split/579-1.html).  The measured
wavelength for a composite object like C-60 will in part depend on the
internal bonds of the molecule.    What then if the corporate object is a
pair of entangled photons?
One of the more fascinating predictions made regarding quantum entanglement
(Jacobson et al., Physical Review Letters, 12 Jun 1995) was the suggestion
that the de Broglie wavelength for an ensemble consisting of N entangled
photons (each with a wavelength of L) would be L/N.  This proposition has
been verified now by physicists at Osaka University (Keiichi Edamatsu,
81-6-6850-6507, eda{at}mp.es.osaka-u.ac.jp) for the case of two entangled
photons.  The daughter photons were created by the process of parametric
down-conversion, in which an incident photon entering a special crystal will
split into two correlated photons.  These photons are then sent through an
interferometer (see figure at http://www.aip.org/mgr/png/2002/169.htm).  The
resultant interference pattern shows that the photons behave as if they
acted as a single entity with a wavelength half that for either photon
alone, a feature which might improve the sharpness of future quantum
lithography (the narrowness of lines on a circuit board being no better than
the wavelength of light used in the fabrication process).  But since the
parent photon already had this shorter wavelength, what will have been
gained by splitting the photon in half?  The advantage will come when, at
some point in the future it will be possible to generate entangled photons
from non-entangled photons of the same wavelength, a process called
hyper-parametric scattering.  (Edamatsu et al., Physical Review Letters, 18
November 2002)

ICICLE INSTABILITY.   No two snowflakes are alike, according to common
wisdom.  Icicles, on the other hand, are all alike--that is, the ripples
that embellish the surfaces of most icicles are similar regardless of
variations in air temperature, humidity, icicle thickness, or growth rate.
An icicle grows when thin sheets of water flow down the icicle shaft. A
portion of the flowing water freezes and the rest drips from the icicle tip.
But the ice that's left behind doesn't build up uniformly; instead, it is
selectively deposited at certain locations. As a result, icicles are covered
in ring-like ripples extending along their lengths, which always measure
about 1 cm from peak to peak. Researchers at Hokkaido University's Institute
of Low Temperature Sciences in Japan (Naohisa Ogawa and Yoshinori Furukawa:
ogawa{at}particle.sci.hokudai.ac.jp, frkw{at}lowtem.hokudai.ac.jp) have
developed a theoretical model that explains the surprisingly universal
structure of icicles. According to the new model, two effects are important
as an icicle grows. The first effect is the Laplace instability, which is
related to the latent heat released from an icicle's surface and dispersed
into the air through the thin water layer.  The instability arises because
heat is more rapidly lost from the convex surfaces than that from the
concave surfaces, which makes ice build up faster on an icicle's convex
protrusions than on the concave indentations, thus amplifying ripples. The
second factor is the fluid effect. Flow in the thin water layer decreases
the temperature distribution along the layer, making it uniform and thus
inhibiting the Laplace instability. As it happens, these two competing
effects ensure that all icicle ripples have the same wavelength, although
the ripple height can vary from one icicle to another. The theory also
predicts that the ripples should migrate down an icicle at about half the
speed that the icicle grows--a prediction the researchers hope will soon be
verified experimentally. In addition the researchers expect that their model
should be helpful in explaining the structures of mineral stalagmites
commonly found in limestone caves. (N. Ogawa and Y. Furukawa, Physical
Review E, October 2002)

POWERFUL T-LUX SPOTTED IN VIRGINIA.  Terahertz radiation, far-infrared
light with frequencies around 10^12 Hz, is difficult to make in useful
amounts with electronic devices.  It is, however, potentially valuable for a
number of important applications, such as performing spectroscopy on
proteins and buried structures in semiconductors.  A new experiment
conducted at the Jefferson Lab free electron laser (FEL) has now produced a
broadband batch of coherent THz light with an average beam power of 20
watts, some 100,000 times better than previous sources.  The T-light is
produced in 500-femtosecond spurts when comparably timed bunches of
electrons pass through a tiny region of magnetic field.  (Carr et al.,
Nature, 14 November 2002.)

***********
PHYSICS NEWS UPDATE is a digest of physics news items arising
from physics meetings, physics journals, newspapers and
magazines, and other news sources.  It is provided free of charge
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Physics News Update appears approximately once a week.

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