Number 138, July 26, 1993 by Phillip F. Schewe and Ben Stein
THE QUANTUM WAVE FUNCTION OF LIGHT has been measured experimentally
by researchers at the University of Oregon and Oregon State (D.T. Smithey
et al, Phys. Rev. Lett., 1 March 1993; contact Michael Raymer, 503-346-4785).
Previous experiments on light and other quantum systems focused on measuring
specific properties such as the mean strength of a light wave's electric
field; none had directly investigated the underlying wave function, which
in principle embodies all information about the quantum system and its
properties. Armed with improvements in detector technology, the Oregon
researchers applied a recent theoretical proposal for determining the wave
function experimentally; they measured electric field amplitudes at different
values of phase in a pulse of light. They made repeated measurements on
identically prepared pulses, building up statistical distributions showing
the range of amplitude values measured at each phase. From these measurements,
they were able to reconstruct the Wigner function, a "quasiprobability"
function which determines the probability distribution for one quantum
property (in this case, the electric field amplitude in phase with a reference
wave) or its complementary quantum property (the electric field amplitude
90 degrees out of phase). More significantly, the measured Wigner function
for this system is essentially the Fourier transform of the wave function.
The wave function, measured in this way, can in principle provide information
about properties not even measured in the experiment, such as the photon
number. These measurements promise to provide new insights into many quantum
phenomena, such as "squeezed light." (Physics World, July 1993.)
THE ANDROMEDA GALAXY HAS A DOUBLE NUCLEUS . Hubble Space Telescope images
show that Andromeda seems to have a small bright nucleus at the true galactic
center and another, brighter, nucleus about 5 light years away. Double-nucleus
galaxies have been seen before, but the usual explanation for this---a
messy merger of two separate galaxies---does not seem appropriate for Andromeda,
which has often served as a textbook example of spiral galaxy structure.
Two Hubble scientists, Tod Lauer of the National Optical Astronomy Observatories
and Sandra Faber of UC Santa Cruz, offer two hypotheses: a lone nucleus
may appear as two if it is partially obscured by dust; or one of the two
nuclei may be the remnant of a smaller galaxy cannibalized by a much larger
galaxy. (The New York Times, 20 July 1993.)
THE LIQUID SCINTILLATOR NEUTRINO DETECTOR (LSND) at Los Alamos will
provide the best terrestrial limits on oscillations between electron- and
muon-type neutrinos; such oscillations may be at least partially responsible
for the "solar neutrino problem" insofar as electron neutrinos
from the sun that turn into muon neutrinos on their way toward the Earth
would not be spotted by detectors sensitive only to electron neutrinos.
At Los Alamos a beam of neutrinos will enter a 9-m-long tank containing
200 tons of liquid scintillator; neutrino and antineutrino interactions
will be signalled by brief bursts of light. Two years of data collection
(starting this summer) should provide limits on neutrino oscillation---expressed
in terms of the square of the mass difference between muon and electron
neutrinos (assuming that at least one neutrino species has a nonzero mass)---of
about 4 x 10**-2 eV**2. (CERN Courier, Jul 1993.)
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