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Number 471, February 17, 2000 by Phillip F. Schewe and Ben Stein
MOLECULES HAVE BEEN FORMED WITHIN A BOSE EINSTEIN CONDENSATE (BEC). First physicists at the University of Texas create a condensate of rubidium atoms in a trap. Then diatomic molecules (dimers) are formed by getting two nearby Rb atoms first to absorb a photon together and then to emit a second photon. This photo-association process eaves the Rb2 dimer essentially at rest, with an equivalent temperature of about 100 nK; "...perhaps the coldest molecules in the universe," says Paul Julienne of NIST (Science News, 12 Feb 2000). The stillness makes possible high precision spectroscopy of the molecules, at a level at least 10,000 times more accurate than for previous experiments in laser-cooled gases. This high resolution allowed the group to measure a molecule condensate interaction for the first time. With further work, this technique could lead to the formation of a molecular BEC, the researchers say. (Wynar et al., Science, 11 Feb 2000.)
QUANTUM MIRAGE. The scanning tunneling microscope (STM) allows one both to push individual atoms around on a surface and to image them. Especially intriguing are images of "quantum corrals," circular or elliptical arrangements on a surface inside of which the waves corresponding to electrons near the substrate surface can be revealed. The latest entry in the gallery of fine pictures comes from IBM, where physicists placed 36 cobalt atoms in an elliptical "Stonehenge" pattern on a copper surface. An extra magnetic cobalt atom was placed at one of the two foci of the ellipse, causing visible interactions with the surface electron waves. But the waves seem also to be interacting with a phantom cobalt atom at the other focus, an atom that is not really there. (Manoharan, Lutz, Eigler, Nature, 3 Feb 2000; see figure at Physics News Graphics.)
FIRST SPACECRAFT IN ORBIT AROUND AN ASTEROID. The Near Earth Asteroid Rendevous (NEAR) spacecraft has arrived at, and gone into orbit around, asteroid Eros, which was at a distance of 160 million miles from Earth when the rendevous occurred. The asteroid, whose gravity is about one thousandth that of Earth, might represent a chunk of matter not much altered from the time the solar system was formed 4 billion years ago, and so it is of great interest to planetary scientists. (NASA press conference, 17 Feb; http://near.jhuapl.edu/iod/20000215/index.html)
ATTOSECOND LIGHT PULSES. A curtailed wave
pulse can be represented mathematically as the weighted sum of a number of wavetrains
of various wavelengths. In this way, scientists at the Foundation for Research
and Technology-Hellas (FORTH) in Crete have created light pulses less than a
femtosecond (10-15 seconds) in duration (Papadogiannis
et al., Physical Review Letters, 22 November 1999). First they split
a beam of light (wavelength of 800 nm ) into two parts; each of these, when
sent through an argon vapor, produces sets of higher-harmonic wavetrains (at
wavelengths equal to several fractions of the original 800 nm) which add together
in a synchronized way to form the ultrashort wave pulse with a duration estimated
to be less than 100 attoseconds. Before this the record short pulse was 4.5
fs in duration. (Physics World,
Feb 2000.)
Since this item was first published, Physical Review Letters has published
a comment on the
paper, and a subsequent reply
by the authors.
UNEMPLOYMENT LEVELS WERE ONLY 2 PERCENT FOR U.S. PHYSICS PHDS receiving their degrees in 1997 and seeking employment in the winter after their graduation, dropping from a recent high of 6% for the class of 1993, according to a new report from the American Institute of Physics. However, most Ph.D.s in permanent positions stated that they were working in an area that was not primarily physics, although this does not mean that their jobs involved little or no physics.
Perhaps surprisingly in the post-Cold War era, bachelor recipients from the
class of 1998 appear to be, if anything, exceedingly hopeful about their long-range
career goals: for example, 61% said they intended to become a college or university
professor, but this is far higher than the percentage historically attaining
this goal. Most employed master's degree recipients from the class of 1997 (62%)
work in industry, with three-fourths viewing their job as being related to physics.
After many years of decreasing steadily, the number of students earning physics
bachelor's degrees has stabilized at least for the time being, with a total
of 3,821 granted in the 1997-98 academic year. (Report available at the AIP
Education and Employment Statistics Division.)
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