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update.356 (fwd)



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>From [email protected] Tue Jan 27 15:31:03 1998
Date: Tue, 27 Jan 1998 08:46:26 -0500
From: [email protected] (AIP listserver)
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To: [email protected]
Subject: update.356


PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 356 January 27, 1998   by Phillip F. Schewe and Ben Stein

LOCALIZATION OF LIGHT has been achieved by an Amsterdam-
Florence collaboration (contact Ad Lagendijk, [email protected]). 
Consider the movement of light through a  diffuse medium such as
milk, fog, or sugar.  The light waves scatter repeatedly, and the
transmission of light decreases as the light gets reflected. In the
Amsterdam-Florence experiment something different happens.  By
using a gallium-arsenide powder with a very high index of
refraction but with very low absorption at near infrared (wavelength
of 1064 nm), the researchers were, in a sense, able to get the light
to stand still.  That is, the light waves get into the medium and
bounce around in a standing wave pattern, without being absorbed. 
This is the first example of "Anderson localization" for near-visible
light.  This medium is not what would be called a "photonic
bandgap" material (analogous to a semiconductor for electrons) but
more like a "photonic insulator." (Wiersma et al., Nature, 18/25
December 1997; see also www.aip.org/physnews/graphics)

QUANTUM EVAPORATION occurs in a new experiment when a
beam of phonons (little pulses of sound issuing from a warm
filament) inside a pool of superfluid helium-4 is aimed at the liquid
surface from below.  In analogy with the photoelectric effect (in
which light ejects electrons from a surface), the phonons pop helium
atoms up out of the liquid.  By measuring the momenta of the
phonons and the evaporated atoms, one can determine that the
atoms originally had zero momentum parallel to the surface,
demonstrating directly (for the first time) that the He-4 atoms had
been part of a Bose-Einstein condensate (BEC), in which the atoms
fall into a single quantum state.  Theories of superfluid He-4 had
supposed that the atoms reside in a BEC state, but this had not been
experimentally verified until now.  The researcher, Adrian Wyatt
of the University of Exeter,  believes this method can be used to
generate beams of coherent helium atoms (an "atom laser" effect). 
(Nature, 1 January 1998.)

ANOTHER VERSION OF QUANTUM TELEPORTATION is
being published by researchers in Italy and England (Francesco
DeMartini, University of Rome, [email protected]).  Like
the Innsbruck teleportation scheme published several weeks earlier
(Update 351), this demonstration employs a pair of entangled
photons.   Whereas the Innsbruck experiment teleported the
polarization value of a third, distinct "message photon" to one of
the entangled photons, the Rome scheme encodes one of the
entangled photons with a specific polarization state and transmits
this state to the other entangled photon. Although different from the
Innsbruck experiment (which had a 25% teleportation success rate)
and the original theoretical proposal for teleportation, this scheme
works 100% of the time if the receiver applies the right
transformations on the second photon. (D. Boschi et al., upcoming
article in Physical Review Letters).  In another, theoretical paper,
Sam Braunstein of the University of Wales (Bangor) and Jeff
Kimble of Caltech propose an experimental method for extending
quantum teleportation from transmitting discrete variables such as
polarization to transmitting continuous variables like the amplitude
of the electric field associated with a light wave. (Braunstein et al.,
Phys. Rev. Lett., 26 January 1998.)