From: Jim Choate <ravage@einstein.ssz.com>
Date: Thu, 15 May 1997 11:59:39 +0800
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Subject: update.321 (fwd)
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>From physnews@aip.org Wed May 14 13:21:46 1997
Date: Wed, 14 May 97 10:24:01 EDT
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Subject: update.321


PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 321 May 13, 1997   by Phillip F. Schewe and Ben Stein

A PHOTON CONVEYOR BELT has been created using sound
waves and lasers, bringing about a new method for processing and
storing light signals on a chip.  In some opto-electronic devices it
is desirable to delay or store an optically-encoded message by
dispatching it down kilometer-long fiber cul-de-sacs.  In a device
developed at the University of Munich, the delay can be
accomplished more compactly by first converting the light into a
splash of excitons (electron-hole pairs) which propagate at a more
leisurely pace, the electrons and holes surfing along on different
parts of a guiding acoustic wave.  Later the electron-hole pairs
recombine into photons, which are read out at the other end of the
sample.  In effect the signal has been converted from a speed-of-
light wave into a speed-of-sound wave, and back again.  This
technique is also a way of prolonging the lifetime of excitons,
which typically live for mere nanoseconds before recombining; in
this experiment they have now been preserved for microseconds.
(C.  Rocke et al., Physical Review Letters, 19 May 1997; contact
Achim Wixforth, Achim.Wixforth @physik.uni-muenchen.de;
animation at www.aip.org/physnews/graphics)

THE QUANTUM WAVEFUNCTION OF A MATTER WAVE,
the complete mathematical description of a quantum system, has
been experimentally reconstructed for the first time.   Trapping a
single beryllium ion in electric fields, Dietrich Leibfried and his
colleagues at NIST created a state in which the ion has exactly one
quantum of vibrational energy. Determining the wavefunction,
which contains all the knowable information about this system, is
difficult because the uncertainty principle says that measuring its
position alters its momentum and vice versa.   But by preparing the
same quantum state 500,000 times and making a different
measurement each time, the researchers sidestepped this limitation
and reconstructed piecemeal the probability for the ion to have
certain values of position and momentum.  Known as the Wigner
function, this "quasiprobability" distribution can be mathematically
transformed into an average quantum wavefunction for the system
which, the researchers argue, is nearly identical to the actual
wavefunction. The NIST researchers were the first to measure
negative Wigner function values for certain coordinates of position
and momentum--something that can only happen for quantum
systems; this reflects the fact that the system can exist in many
states simultaneously. (Physical Review Letters, 18 November
1996.)   Subsequently, physicists at the University of Konstanz in
Germany measured the Wigner function of a matter wave traveling
in free space--a helium atom traversing a pair of slits.  (Nature, 13
March; also Science News, March 15.)

PHYSICISTS ARE 46 YEARS OLD AND MAKE $65,000 A
YEAR.  These are median values for a PhD physicist in  the U.S.
in 1996.  Those who work at federal labs made the most (median 
$78,500), even more than in industry (median $77,000); those at 
4-year colleges made the least, with a median of $49,200. 
Geographically, median salaries ranged from $70,000 (Pacific
states) to $56,200 (East South Central). New PhD's earn $31,000
at universties and $39,600 at federal labs.  Salaries for female
physicists who have earned the PhD in the past 10 years are
comparable to salaries for male physicists with similar experience
("Society Membership Survey: Salaries 1996," a report issued in
April by the AIP Education and Employment Statistics Division;
contact Ray Chu, rchu@aip.org)