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From physnews@aip.org Tue Jan 27 15:31:03 1998 Date: Tue, 27 Jan 1998 08:46:26 -0500 From: physnews@aip.org (AIP listserver) Message-Id: <199801271346.IAA15741@aip.org> To: physnews-mailing@aip.org Subject: update.356
PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 356 January 27, 1998 by Phillip F. Schewe and Ben Stein LOCALIZATION OF LIGHT has been achieved by an Amsterdam- Florence collaboration (contact Ad Lagendijk, adlag@phys.uva.nl). Consider the movement of light through a diffuse medium such as milk, fog, or sugar. The light waves scatter repeatedly, and the transmission of light decreases as the light gets reflected. In the Amsterdam-Florence experiment something different happens. By using a gallium-arsenide powder with a very high index of refraction but with very low absorption at near infrared (wavelength of 1064 nm), the researchers were, in a sense, able to get the light to stand still. That is, the light waves get into the medium and bounce around in a standing wave pattern, without being absorbed. This is the first example of "Anderson localization" for near-visible light. This medium is not what would be called a "photonic bandgap" material (analogous to a semiconductor for electrons) but more like a "photonic insulator." (Wiersma et al., Nature, 18/25 December 1997; see also www.aip.org/physnews/graphics) QUANTUM EVAPORATION occurs in a new experiment when a beam of phonons (little pulses of sound issuing from a warm filament) inside a pool of superfluid helium-4 is aimed at the liquid surface from below. In analogy with the photoelectric effect (in which light ejects electrons from a surface), the phonons pop helium atoms up out of the liquid. By measuring the momenta of the phonons and the evaporated atoms, one can determine that the atoms originally had zero momentum parallel to the surface, demonstrating directly (for the first time) that the He-4 atoms had been part of a Bose-Einstein condensate (BEC), in which the atoms fall into a single quantum state. Theories of superfluid He-4 had supposed that the atoms reside in a BEC state, but this had not been experimentally verified until now. The researcher, Adrian Wyatt of the University of Exeter, believes this method can be used to generate beams of coherent helium atoms (an "atom laser" effect). (Nature, 1 January 1998.) ANOTHER VERSION OF QUANTUM TELEPORTATION is being published by researchers in Italy and England (Francesco DeMartini, University of Rome, demartini@axcasp.caspur.it). Like the Innsbruck teleportation scheme published several weeks earlier (Update 351), this demonstration employs a pair of entangled photons. Whereas the Innsbruck experiment teleported the polarization value of a third, distinct "message photon" to one of the entangled photons, the Rome scheme encodes one of the entangled photons with a specific polarization state and transmits this state to the other entangled photon. Although different from the Innsbruck experiment (which had a 25% teleportation success rate) and the original theoretical proposal for teleportation, this scheme works 100% of the time if the receiver applies the right transformations on the second photon. (D. Boschi et al., upcoming article in Physical Review Letters). In another, theoretical paper, Sam Braunstein of the University of Wales (Bangor) and Jeff Kimble of Caltech propose an experimental method for extending quantum teleportation from transmitting discrete variables such as polarization to transmitting continuous variables like the amplitude of the electric field associated with a light wave. (Braunstein et al., Phys. Rev. Lett., 26 January 1998.)