 |
Aktuelle Meldungen bei MM-Physik 9. November 2001 © email: Krahmer |
|
Aktuelle Meldungen bei MM-Physik 9. November 2001 © email: Krahmer |
"The American Institute of Physics Bulletin of Physics News" AIP Auswahl Oktober 2001 by Phillip F. Schewe and Ben Stein, and James Riordon
 |
Wed, 26 Sep 2001 ENTANGLEMENT OF MACROSCOPIC OBJECTS, a pair of gas clouds containing a trillion atoms each, has been achieved by a research team in Denmark (Eugene Polzik, University of Aarhus, 011-45-89423745, polzik@ifa.au.dk), constituting by far the largest material objects entangled on demand and paving the way for quantum teleportation between macroscopic objects. The accomplishment, published in this week's issue of Nature (Julsgaard et al., 27 September 2001), was announced in preliminary form this June at the first International Conference on Quantum Information, sponsored in part by the Optical Society of America and the American Physical Society. One of the most profound features of quantum mechanics, entanglement is a special interrelationship between objects in which measuring one object instantly influences the other, even if the two are completely isolated from one another. No previous entanglement with atoms has involved more than four particles. Furthermore, atoms have only been entangled at close proximity, either as ions spaced microns apart in a tiny trap (Update 475), or atoms flying over a short range through narrowly spaced cavities (Hagley et al., Phys. Rev. Lett., 7 July 1997). In the present experiment, researchers sent a light beam through two cesium gas samples, each held in a special paraffin-coated cell. The beam changed each sample's "collective spin," which describes, in a sense, the net direction in which all of the atoms' tiny magnets add up. First, the researchers measured the sum of the two collective spins without knowing the individual collective spin of each sample. A subsequent measurement, nearly a millisecond later, showed that the sum remained the same. This demonstrated that the two gas samples maintained their special interrelationship and were entangled. Although the two samples were just millimeters apart, they could in principle be separated, and thereby entangled, at much longer distances. Entanglement of such large objects enables "bulk" properties, like collective spin, to be "teleported," or transferred, from one gas cloud to another. Wed, 31
Oct 2001 |
| 7 Nov 2001 PYROELECTRIC ACCELERATOR. In a pyroelectric crystal held below a critical temperature (the Curie temperature) heating or cooling causes distortions in the lattice of atoms which in turn creates strong electric fields at the surface of the crystal. James Brownridge of the State University of New York at Binghamton (jdbjdb@binghamton.edu) and Stephen Shafroth of the University of North Carolina ( 919-962-3015, shafroth@physics.unc.edu) have used these electric fields to create stable, self-focused electron beams with energies as high as 170 keV. The energy conversion is not especially efficient: inputting watts of heating energy produces only microwatts of output electron beam energy, but this might not be important. Pyroelectric crystals (such as those made of LiNbO3) are widely used as detectors of infrared and THz radiation, but the discovery by Brownridge that they can also be used to produce energetic electron beams if heated or cooled in dilute gas atmospheres means that they can be used to produce x-ray fluorescence for elemental analysis of complex materials, such as tree leaves, rocks, air filters, blood samples, etc. Portable economical x-ray fluorescence is now a real possibility. (Applied Physics Letters, 12 Nov; http://www.binghamton.edu/physics/brownridge.html ) |
|
Wed, 26 Sep 2001 THE BLACK HOLE OF GENEVA. Black holes are known as the omnivorous destroyers of stars. In reality black holes not only take but give. Near their event horizons, where space is so drastically warped, black holes spawn particle-antiparticle pairs out of sheer vacuum. In some cases one of the pair escapes beyond the horizon while its counterpart is pulled back into the hole. Thus black holes can shed energy in the form of this "Hawking radiation." Physicists hope to bring this whole process down to earth by manufacturing tiny black holes amid the stupendous smashups of protons at the Large Hadron Collider (LHC) being built at CERN. Until recently theorists thought gravity was so weak compared to the other forces that it, and gravitationally bound objects like black holes, could be studied on an equal footing with the other forces like the strong nuclear force only at energies of 10^19 GeV. In the past few years, though, some models featuring extra spatial dimensions hint that the unification of the forces, including gravity, might set in at much more modest energies, even in the TeV realm of the LHC. Thus one can contemplate forming a TeV- mass black hole even as one can imagine creating new particles in that mass range. But what would a black hole look like? Savas Dimopoulous of Stanford (650-723-4231) and Greg Landsberg of Brown University (landsberg@hep.brown.edu, 401-863-1464) have drawn a picture in which proton-proton collisions could create black holes with a cross section (likelihood of creation) only about a factor of ten less than for producing top quarks and at a rate of up to one per second (see figure at http://www.aip.org/mgr/png ). A black hole produced in this way would quickly decay, not in the usual particle way but in a furious burst of Hawking radiation. A particularly striking signature of the black hole would involve an electron, muon, and photon in the final state of debris particles. Properties of Hawking radiation could tell physicists about the shape of extra spatial dimensions. A possibility of recreating the early moments of the universe in the lab would further unite particle physics and cosmology (Physical Review Letters, 15 October 2001; text at http://www.aip.org/physnews/select) Wed,
3 Oct 2001
|
 |
Tue, 23 Oct 2001 IMPLANTABLE BioMEMS. Microelectromechanical systems (MEMS), tiny devices crafted using microchip technology, have appeared in a number of settings; examples include micron-sized motors, gears, pumps, and detectors. One would also like to use MEMS in implantable medical applications, but bio-compatibility has been a problem. To address this obstacle Tejal Desai at the University of Illinois-Chicago (tdesai@uic.edu, 312-413-8723) has developed a capsule containing insulin-secreting cells. The capsule is covered with pores as small as 7 nm which allow the release of insulin while blocking the entrance of antibodies thrown up the immune system to counteract the transplanted cells. Desai, who has tested her capsules on mice and rats, will report her new results with nanopore capsules (including also compartmented 100-micron chips for drug delivery) at the AVS Science and Technology Society meeting in San Francisco, Oct 29-Nov 2 http://www.avssymposium.org/Overview.asp Desai's abstract at : http://www.avssymposium.org/paper.asp?abstractID=145 her university website: http://www.uic.edu/depts/bioe/faculty/tejal_desai/CML%20lab/res_lab.htm 7 Nov 2001 SOUND WAVES MAKE FILTERS FINER. Generally, filters that remove particulates from fluids are limited by their pore sizes. That is, a filter with millimeter-sized pores isn't likely to catch many micron-sized particles. On the other hand, a filter with tiny pores can trap small particles at the expense of inhibiting fluid flow. Donald Feke (Case Western Reserve University, dlf4@po.cwru.edu, 216-368-2750), however, has found a way to reduce the effective pore size in highly porous media without significantly hindering fluid flow. By applying a low power acoustic signal to a filter, Feke can trap particles as much as a hundred times smaller than the nominal filter pore size. An acoustically aided filter provides relatively little resistance to the fluid that passes through it, and yet collects particles as efficiently as a much finer filter. And once the filter has done its job, the trapped particles can be released at the flip of a switch that cuts off the acoustical signal (figures at http://www.aip.org/mgr/png ). The trapping arises because acoustic signals traveling through a porous material create patterns of standing waves that focus particulate matter toward certain positions on the walls of the pores. Rather than wending their way through the filter, particles headed for the focal points line up to form intricate, stable filaments. In other locations, groups of particles collect in regions of stability within the pores, where they orbit for as long as the signal persists. In addition to novel filter designs, Feke proposes that acoustic manipulation may lead to efficient material sorting technologies or methods that aid in assembling microscopic structures. Feke presented his work at the 73rd annual Society of Rheology meeting in Bethesda, Maryland. http://www.rheology.org/sor01a/abstract.asp?PaperID=157 |
