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Number 416, February 26, 1999 by Phillip F. Schewe and Ben Stein
WIRE-GUIDED ATOMS. The development of "atom optics" is part of the effort to store, guide, focus, reflect, and perform calculations with atoms in analogy with the ways electrons are used in electronics and photons in photonics. In a new innovation cold lithium atoms from a magneto-optic trap (MOT) were nudged in the direction of a thin current-carrying wire. Although the atoms are neutral, they still feel the magnetic force field which can be used to send the atoms in two types of trajectory. In one case the atoms spiral in "Kepler" like orbits around and along the wire. In the second case the use of an extra field helps to create a "potential tube" parallel to the wire in which the atoms are guided along the side of the wire. This second guide is especially interesting since the wires can be mounted on a surface, allowing for easy miniaturization of these guides and traps. Physicists at the University of Innsbruck (Joerg Schmiedmayer, joerg.schmiedmayer@uibk.ac.at, 011-43-512-507-6306) expect that this will allow them to design guides and traps for cold atoms with a variety of different geometries. These can be used to manipulate atoms from Bose-Einstein condensates, or serve as beam splitters or interferometers for guided atoms. Even more complicated integrated atom optics devices and networks, similar to integrated circuits for electrons, can be devised. Some mesoscopic experiments which now use electrons in solids might, with this new atom optics tool, be able to use guided atoms moving above a surface. (Denschlag et al., Physical Review Letters, 8 March 1999; see figure at Physics News Graphics and Physical Review Focus for 28 July 1998.)
HOLOGRAMS OF TRANSISTOR INTERIORS can provide maps of electrostatic potentials in that crucial zone beneath the transistor's gate, where the passage of electrons from emitter to drain can be made difficult or easy, just as a water tap can switch a faucet on and off. Why are such maps necessary? "Within a decade, integrated circuits will consist of transistors 150 atoms long and 50 atoms deep," according to researchers at the Institute for Semiconductor Physics in Frankfurt (Oder), Germany, and knowledge of the precise whereabouts of dopant atoms will be vital. To this end, the Frankfurt scientists (Wolf-Dieter Rau, rau@ihp-ffo.de, 011-49-335-562-5432) can now produce a subsurface sectional map of the transistor. Electron waves from a transmission electron microscope (in which the quantum wavelike properties of electrons are more important than their particle properties) pass through the thin transistor, where they scatter slightly. These waves are recombined with some unscattered electron waves to form a holographic signal which encodes information about local conditions throughout the section. The electron data can be processed into 2-dimensional images with 10-nm resolution and high sensitivity. (Rau et al., Physical Review Letters, 29 March; see figure at Physics News Graphics)
A SINGLE-PHOTON TURNSTILE, a device in which photons are emitted one at a time under controlled circumstances, has been created by a team of scientists from Stanford (US), Hamamatsu Photonics (Japan), and NTT (Japan). Essentially the researchers use the quantization of electrical conductance to produce a quantization of photon emission. They put together a quantum well (the frontier between two thin semiconductor layers) containing a single electron (other electrons are dissuaded from entering because of a "Coulomb blockade" effect) with a quantum well containing a lone (comparably Coulomb blockaded) hole, and then cycle the voltage across the whole stack of layers in such a way that the lone electron and lone hole meet, mate, and make a lone photon. The resulting device, which operates at mK temperatures, is typically a tiny post some 700 nm tall and with a diameter of 200-1000 nm. (J. Kim et al., Nature, 11 February 1999.)
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