Physics News Update, Number 429

Number 429, May 20, 1999 by Phillip F. Schewe and Ben Stein

THE BIGGEST LAVA OUTPOURING in history probably took place about 200 million years ago. A team of geophysicists has just put together the final jigsaw piece in a puzzle relating separated basaltic layers in spots as far flung as the Hudson River Palisades, Brazil, Europe, and Africa. What started out as an Australia-sized blacktop in the heart of the ancient super-continent Pangea was later torn asunder by the tectonic forces, which carried the fragments to places all around the Atlantic rim, making discovery difficult until now. The immense flow, now referred to as the Central Atlantic Magmatic Province, might have played a part in the mass extinctions occurring at the boundary between the Triassic and Jurassic eras. (Marzoli et al., Science, 23 April 1999).

RYDBERG SCULPTING is a new technique for placing an atom (a highly excited, or "Rydberg," atom) in many energy states simultaneously. Applications could include improved designs for quantum computers, which presently call for collections of rudimentary 2-level quantum systems, similar to the 2-state (0 and 1) classical binary computers used today. But how would an atom be in, say, 10 energy states at one time? By being struck by laser pulses of very short duration. Such a pulse is itself really a superposition of coherent light waves at many different energies. This multi-personality existence is transferred to the atom when it absorbs the laser pulse. In Philip Bucksbaum's lab at the University of Michigan (734-764-4348), actively shaped ultrashort light pulses hit atoms in a beam. This creates within the atom what Bucksbaum calls "wave packet sculpting," a bundle of electron waves dancing in a complex pattern as they go around the nucleus, at times interfering with each other. This interference can already be controlled so carefully that it can be used to store several bits of information. More complex versions will allow the type of factoring or searching exercises (e.g., hunting for a pea hidden under one of several cups) used in quantum computations. Bucksbaum estimates that a number as large as 2¹⁰ could be factored by setting a single atom to work. Factoring larger numbers would require additional atoms. (Paper QTHA1, May 27, at the Conference on Lasers and Electro-Optics (CLEO) meeting in Baltimore. View movie at Physics News Graphics; also see Physical Review Focus, 22 June 1998.)

SUPERCONDUCTIVITY GOES PLATINUM. It is ironic that some of the best insulators (e.g., perovskite ceramics) should make the best superconductors while some of the best conductors (the noble metals gold, silver, and copper) should be bad superconductors. Indeed the electron-phonon interactions that bring about low-temperature superconductivity is so weak in these metals that they have never been seen to superconduct. Recently, though, physicists at the University of Bayreuth (Reinhard Koenig, 011-49-921-55-3340, reinhard@btp9x5.phy.uni-bayreuth.de) in Germany have overcome the recalcitrance of one of those metals, platinum, which became superconducting only at milli-kelvin temperatures. The platinum was studied in the form of a compacted powder which contained only very few magnetic impurities (magnetism being detrimental to superconductivity). Furthermore, it has a much larger surface area, and it is thought that surface vibrations (phonons) may also be important for superconductivity in the platinum powder. This work allows the chance to see how magnetism and superconductivity compete with each other and to study the mechanism of the coupling between superconducting grains of the powder (R. Koenig, A.Schindler, T. Herrmannsdoerfer, Physical Review Letters, 31 May 1999).