Physics News Update Number 261

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Number 261, March 6, 1996 by Phillip F. Schewe and Ben Stein

SQUEEZED PHONONS . By using ballistic sound pulses--- directional sound waves that move considerable distances without scattering---as probes, physicists have learned to image certain internal features of crystals such as point defects. Indeed, the advent of "phonon optics," including the development of phonon mirrors, filters, lenses, and other acoustical analogues of classical optical elements, has given scientists a new way of looking inside solids. Another optical phenomenon, from the realm of quantum optics, may also have an acoustic analogue. In "squeezed light" (created by passing short laser pulses through special crystals) the uncertainty in the amplitude of a laser beam can be reduced to a level below that normally allowed by the Heisenberg uncertainty principle, a level known as the zero-point quantum noise level. This increased knowledge comes at the expense of greater uncertainty in the frequency of the light. Squeezed light may have applications in data transmission and in high-precision metrology. Now, Franco Nori (313-764-3271) at the University of Michigan suggests that this same idea can be applied to phonons. Keeping in mind that a phonon traveling through a solid is equivalent to the propagation of a slight disturbance in the local arrangement of atoms in the solid, then the creation of squeezed phonon states would lead to the possibility of reducing the quantum fluctuations of atomic displacements to below the zero-point noise level. (Xuedong Hu and Franco Nori, Physical Review Letters, 25 March 1996.)

X-RAY BURSTER/PULSAR. The first object known to be both an x-ray pulsar (emitting regular pulses twice a second) and an x- ray burster (whose transient bursts---up to 18 an hour---make it at times the brightest celestial x-ray emitter) has been detected by the Gamma Ray Observatory. First spotted in December 1995 near the galactic center, the object GRO J1744-28 is believed by some theorists, such as Don Lamb at Chicago, to be a binary star system in which the material from a dying normal star is being siphoned away by a nearby neutron star. The infall of the material might be igniting thermonuclear explosions at the surface of the neutron star. (C. Kouveliotou et al., Nature, 29 Feb. 1996; news item in Science, 23 Feb.)

BEAM CHANNELING AT 900 GEV. At accelerators, charged- particle beams are usually steered with powerful magnets. But years ago physicists discovered that a beam could also be deflected by passing it down the alleyways between the rows of atoms in a bent crystal. Recently scientists at the Tevatron Crystal Extraction Experiment succeeded in diverting the 900-GeV beam at Fermilab through a 4-cm-long crystal shaped into a 640-microradian bend. (CERN Courier, Jan/Feb 1996.)

PHDs ARE UP BUT 1ST-YEAR STUDENTS ARE DOWN , suggesting a coming downturn in physics PhDs at U.S. universities. A new AIP report, "Enrollments and Degrees Report" (January 1996), shows that physics PhD production continues to rise: 1481 were granted in 1994, compared to 1369 the year before. But the number of 1st-year graduate students is down 22% at PhD-granting institutions and juniors are down 13% since 1992. (For more information contact Patrick Mulvey, 301- 209-3076.)