Forwarded message:
From physnews@aip.org Wed Oct 30 17:36:20 1996 Date: Wed, 30 Oct 96 13:58:39 EST From: physnews@aip.org (AIP listserver) Message-Id: <9610301858.AA27601@aip.org> To: physnews-mailing@aip.org Subject: update.293
PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 293 October 30, 1996 by Phillip F. Schewe and Ben Stein SIGNAL TRANSMISSION THROUGH A MAMMALIAN NERVE-CELL NETWORK can be enhanced with the help of electrical noise, a new experiment has shown. First proposed to explain the periodicity of ancient ice ages (in which the random "noise" of climate variations may have augmented the effects of predictable Earth-Sun distance variations from year to year) and first experimentally demonstrated in lasers (in which the direction of laser light traveling around a loop was switched from clockwise to counterclockwise by adding acoustical noise to the crystal from which the light emerged), the phenomenon of "stochastic resonance" (SR) describes how introducing a certain amount of noise into a system can actually enhance the transmission or detection of a weak signal so as to maximize the ratio of signal to noise. In the first demonstration of SR in mammalian tissue, researchers (Mark Spano, Naval Surface Warfare Center, 301-227-4466) apply a weak electric signal (containing both signal and noise) to a slice of rat hippocampus, a brain region essential for memory and other tasks. With the slice parallel to the plane in which nerve cells convert incoming signals into electrical nerve impulses, the researchers could transmit a weak signal to all nerve cells in the network. At an optimal noise intensity a maximum in the signal-to-noise ratio was reached--a hallmark of SR. This experiment offers the intriguing possibility that SR may potentially be exploited to aid transmission, detection and processing of signals in neuronal networks. (B.J. Gluckman et al., Physical Review Letters, 4 November 1996.) A QUANTUM COMPUTER COULD TOLERATE ERRORS while carrying out calculations, researchers at Los Alamos have now shown. Computers that operated according to the rules of quantum mechanics have the potential to perform powerful tasks (such as factoring huge numbers) because of their radically different approach to logic: unlike a conventional computer's bits, which exist either as a 0 or a 1, a quantum bit (or "qubit") could not only exist simultaneously as a 0 and a 1 but could interact with other qubits so that its properties became "entangled" with those of the other qubits. Yet some physicists argue quantum computers may be impossible to achieve on a practical level because the slightest amount of noise would destroy the entanglement and thus corrupt the state of the qubits. Up to now, proposed "quantum error correction" schemes have shown merely how to preserve the state of qubits. Now, Los Alamos researchers (Raymond Laflamme, 505-665-3394) have developed an algorithm for carrying out reliable calculations on a "qubyte" made of 7 entangled qubits while accounting for the possibility that one of the qubits is corrupt (upcoming paper in Phys Rev Lett). Experimentally, quantum computing is regarded as a long-term possibility: although quantum versions of logic gates have been constructed (see Update #250), researchers are still working to entangle more than two quantum systems at a time. A PHOTOELECTROCHROMIC (PEC) cell harnesses a photochromic layer, which changes color by absorbing light, with an electrochromic layer, which changes color under the influence of an electric field, to make a self-powered smart window. On a sunny day the one layer supplies the photovoltage needed by the other layer to darken the window, letting in less light and thus lowering air- conditioning costs. This photoelectrochromic process, developed by scientists at the National Renewable Energy Lab in Golden, Colorado, might also be useful in display applications. (C. Bechinger et al., Nature, 17 October 1996.)