Number 234, July 21, 1995 by Phillip F. Schewe and Ben Stein
NEW OSCILLATION MODES IN THE SUN have been discovered by studying Ulysses
and Voyager measurements of solar wind particle fluxes. Looking at flux
levels recorded over years, three scientists at AT&T Bell Labs have
discerned periodicities in the data. They assert that some of the features
correspond to pressure (or p-mode) oscillations---essentially standing
acoustic waves at the sun's surface---previously known from direct visual
observations. But other, unexpected, patterns in the data, with periods
of days or hours, also suggest the existence of hypothesized gravity (or
g-mode) oscillations, which may well arise from the solar core, where fusion
reactions occur and solar neutrinos originate. If this interpretation is
substantiated, then measurements of the solar wind might serve as a probe
of the deep solar interior. The Bell Labs researchers have tried to explain
how disturbances at the solar core could be transcribed into variations
in the solar wind. They suggest that the g modes influence the solar wind
by helping to shape the solar magnetic field. (David J. Thomson et al.,
Nature, 13 July 1995.)
INTERFEROMETRY OF ELECTRON WAVES WITHIN AN ATOM. Light waves passing
through a pair of slits in a screen will interfere with each other and
produce a characteristic pattern of light and dark areas on a photographic
film. Exploiting the wave nature of particles, physicists have also performed
this experiment ("Young's double-slit experiment") with electrons
and even atoms. Carlos Stroud ((716-275-2598) and Michael Noel at the University
of Rochester have now carried out interferometry within a single atom by
causing a single electron to interfere with itself. First, they use a short
laser pulse to excite a potassium atom into a so-called Rydberg wave packet
state, a condition in which the outermost electron (although still attached
to the nucleus) has a finite probability of residing in a classical Keplerian
orbit (i.e., at times the electron's orbit is like that of a planet around
the sun) as far away as half a micron (compared to a more typical distance
of an angstrom). A second laser pulse, related to but delayed relative
to the first pulse, further enhances the probability of the electron to
be in the outer-lying orbit, although in a different location. One can
think of this sequential laser excitation as establishing two spatially
separate wave packets, which according to quantum mechanics correspond
to the probability that the electron will be located in two particular
locations in space. In the course of time, the waves in these packets spread
out and interfere, just as the light waves emerging from the Youngs' slits
interfere. The Rochester physicists then probe the interference pattern
at later times with yet a third laser pulse. They find that by varying
the relative phases of the laser pulses they can control whether the electron
is on one side of its orbit or the other, a half micron away. Although
they still possess quantum properties, the electrons in a Rydberg wave
packet state also behave in a sort of quasi-classical way like particles
traveling in large elliptical orbits. Scientists in this research area
are seeking to learn more about the frontier between quantum and classical
physics. (Michael W. Noel and C.R. Stroud, 14 Aug. 95, Physical Review
Letters; journalists can obtain the text and figures by contacting AIP
Public Information at 301-209-3091 or physnews@aip.org. Unfortunately,
we cannot supply the article to non-journalists.)
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