>Date: Fri, 17 Mar 2000 10:43:27 -0500 (EST)
>From: AIP listserver <[EMAIL PROTECTED]>
>To: [EMAIL PROTECTED]
>Subject: update.475
>
>PHYSICS NEWS UPDATE
>The American Institute of Physics Bulletin of Physics News
>Number 475 March 17, 2000 by Phillip F. Schewe and Ben Stein
>
>STRANGE HALO ORBITS EXPECTED AT SATURN. Consider
>particles in orbit above a planet. If the particles are uncharged or have a
>very low charge-to-mass ratio, they will follow a conventional
>("Keplerian") trajectory centered about the axis of the planet at the equator
>(Saturn's rings are an example of such particles). If, however, the
>particles are highly charged, their motions are dominated by an
>electromagnetic interaction with the planet's magnetic dipole (Earth's van
>Allen belts are an example). If the charge is somewhere in between these
>two cases, and gravity and electromagnetic forces are comparable, then
>strange orbits are possible. Scientists at the University of Colorado
>(Mihaly Horanyi and Jim Howard, 303-492-6903) and Loughborough
>University (Holger Dullin) in the UK estimate that if conditions are just
>right some particles could race around a planet in orbits (stable for as long
>as 10 years) that never cross the planet's equatorial plane (see figure at
>www.aip.org/physnews/graphics). The dust analyzer on the Cassini craft
>now gliding toward Saturn might be able to detect particles in these novel
>orbits. (Howard et al., upcoming article in Physical Review Letters;
>Select Article.)
>
>THE FIRST ENTANGLEMENT OF FOUR PARTICLES has been
>experimentally achieved by researchers at NIST (Christopher Monroe,
>303-497-7415), demonstrating a technique that significantly advances the
>difficult prospect of building a useful quantum computer. To perform
>powerful calculations, such as factoring huge numbers or quickly finding
>items in large databases, a quantum computer typically must contain many
>particles "entangled" with each other. Entanglement describes a very
>special interlinking that can occur between particles (such as photons or
>ions) even if they are physically separated or otherwise isolated from one
>another. While entangled, each particle is in a fuzzy, noncommital state
>(for example, being in a combination or "superposition" of a low and high
>energy state) but has a precisely defined relationship with its partners.
>Specifically, when one particle eventually "collapses" into a definite state,
>it essentially causes its entangled partner to collapse into a complementary
>state, even if it is halfway across the galaxy. Entanglement is difficult
>enough to achieve in two particles, or even three (Update 414), but last
>year, theorists in Denmark proposed a practical method for entangling any
>number of particles. (Molmer and Sorensen, Phys. Rev. Lett., 1 Mar 1999;
>see article at Physics News Select Articles.) Their proposal, based in turn
>on a earlier idea (Cirac and Zoller, Phys. Rev. Lett, 15 May 1995),
>involves trapping a string of ions in electromagnetic fields. To create
>multiple entanglement, laser pulses can interlink each ion's internal state
>(known as its spin) to the overall motion of the ions rocking back and
>forth. The Molmer-Sorensen technique enables researchers to accomplish
>this in a single pulse. NIST researchers demonstrated this technique with
>four ions (electrical noise made it difficult to do more), but they showed
>that entanglement of many more particles is now possible. (Sackett et al,
>Nature, 16 March 2000.)
>
>REMOVING A COMMUNICATIONS BOTTLENECK WITH
>INKJETS. At last week's Optical Fiber Communication Conference, held
>in Baltimore by IEEE and the Optical Society of America, researchers
>from Agilent Technologies (a spinoff of Hewlett Packard) unveiled
>technology that makes possible a faster, all-optical communications
>network. Currently, fiber optics networks are not completely optical.
>Traditional switches for re-routing a fiber-optic signal are devices that
>convert photons into electrons and then back into photons. However, the
>new device employs a specially designed "planar-lightwave circuit"--a flat
>circuit through which multiple light signals can travel. The waves
>converge at "cross points" filled with a fluid possessing the same optical
>properties as the rest of the material. Through the fluid, optical signals
>can pass through undisturbed. Rerouting the signal is accomplished by
>injecting an inkjet bubble at the cross point. The bubble displaces the
>fluid and changes the optical properties of the cross point, enabling the
>signal to switch direction. The bubbles, which can be added and removed
>hundreds of times a second, thereby allow signals to be rerouted without
>any moving parts or mirrors, let alone electrons. This "Photonic Switching
>Platform" should be available commercially by the end of the year. (For
>more details, see http://www.agilent.com/about/feature/photonic.html)
>
