update.519 (fwd)

[Jim Choate]

    ____________________________________________________________________

           Before a larger group can see the virtue of an idea, a
           smaller group must first understand it.

                                           "Stranger Suns"
                                           George Zebrowski

       The Armadillo Group       ,::////;::-.          James Choate
       Austin, Tx               /:'///// ``::>/|/      ravage at ssz.com
       www.ssz.com            .',  ||||    `/( e\      512-451-7087
                           -====~~mm-'`-```-mm --'-
    --------------------------------------------------------------------

---------- Forwarded message ----------
Date: Thu, 4 Jan 2001 13:25:48 -0500 (EST)
From: AIP listserver <physnews at aip.org>
To: physnews-mailing at aip.org
Subject: update.519

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 519  January 4, 2001   by Phillip F. Schewe and Ben
Stein          

PHYSICS NEWS STORIES OF THE YEAR.  Our top three
stories represent one definite sighting and two near misses: the
discovery of the tau neutrino (Update 495) and the report of
statistically-poor but fascinating evidence for quark-gluon plasma
(Update 470) and the Higgs boson (502).  Other top physics
events for the year 2000 include (in roughly chronological order
through the months) the resolution of the astrophysical x-ray
background into discrete sources (467); the ability to guide atoms
around "atom chips" (469, 486); all-optical NMR (472); quantum
entanglement of 4 ions in a trap (475); the fabrication of a "left-
handed" composite material, one possessing both a negative
electrical permittivity and a negative magnetic permeability (476);
the best map yet of the cosmic microwave background, showing
that the curvature of the universe is zero (479, 481); the
observation of quantum heat, particles of thermal energy moving
down wires (481); the best measurement, by a factor of 10, of the
gravitational constant G (482), with a corresponding adjustment in
the mass of the Earth; the first-time measurement of gravity at the
micron distance scale as part of the search for extra dimensions
(483); the quantum superposition of superfluid currents flowing in
both directions through a SQUID (492); a record number of
daughter particles made in heavy-ion collisions at RHIC (505);
numerous advances  in quantum cryptography (480); light slowed
to 1 mph (472); advances in delivering drugs and genes with
ultrasound-activated bubbles (487); and the discovery that
entangled photons can defeat the diffraction limit (503).

NONCLASSICAL LIGHT.  A feature of quantum theory is that
objects should have both particle and wave properties.  Thus,
things usually encountered as particles such as electrons or atoms
show their quantum, or nonclassical, nature in the form of
wavelike effects.  Conversely, light, which can usually be
described by a wave equation, shows its nonclassical side by
acting like a particle.  In most optics experiments, even those
involving lasers, the light produces only classical effects which
can be described using 19th century electromagnetism.  For
example, a grocery scanner diode laser emits about 10^15 photons
per second.  When such a stream encounters a half-silvered
mirror, half of the light will be reflected, and half transmitted. 
With so many photons, the individual particle nature is hidden
when the photons are detected at photodiodes sitting behind each
exit port of the beamsplitter. If the original laser beam is replaced
with a source of single photons, then the story is different: a lone
photon might well have an equal chance of going towards either
detector, but it will ultimately register in only one, a sure sign of
quantum behavior.  One can probe these issues more deeply by
using entangled photon pairs.  Kevin Resch, Jeff Lundeen, and
Aephraim Steinberg at the University of Toronto send ultraviolet
(UV) light into a special crystal in which a single UV photon can
produce two red photons in a process called down-conversion. 
One of the red photons is vertically polarized and the other is
horizontally polarized, and therefore the photons can be time-
delayed relative to one another by varying the thickness of
birefringent material (which can swivel a light wave's orientation)
traversed by the photon.  By adjusting the delay between the
photons, the researchers were able to change the number of
photon pairs emerging from an interferometer without changing
the intensity, or brightness, of the beam.  Owing to the intrinsic
nonlinear response of the detectors this quantum interference
effect then became apparent in the counting rate at a single
detector (an effect never before observed) and not just in the
coincidence rate between a pair of photodetectors.  The
researchers believe that the ability to observe such nonlinear
responses in photodetection at the single photon level may be
useful to the study of decoherence in photodetection and for
providing an experimental basis for developing a more accurate
theoretical description for photodetection.  (Physical Review A, 1
February 2001; Kevin Resch contact: 416-946-3162,
resch at physics.utoronto.ca.)