Forwarded message:
From physnews@aip.org Fri Jun 14 18:39:08 1996 Date: Fri, 14 Jun 96 16:45:16 EDT From: physnews@aip.org (AIP listserver) Message-Id: <9606142045.AA11832@aip.org> To: physnews-mailing@aip.org Subject: update.275
PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 275 June 14, 1996 by Phillip F. Schewe and Ben Stein THE FIRST QUANTUM COMMUNICATION USES "TRITS" INSTEAD OF BITS. For the first time, physicists have exploited the laws of quantum mechanics to send data, and with their technique have conveyed information more efficiently than with traditional means. In contrast to a traditional computer, in which messages consist of tiny electric pulses encoded in binary form (i.e., streams of 0s and 1s), researchers at the University of Innsbruck in Austria send messages consisting of single photons which can be coded as 0s, 1s, and 2s, setting up a base three system called "trits." The Innsbruck group (Harald Weinfurter, harald.weinfurter@uibk.ac.at) converts a single ultraviolet photon into two photons whose properties are quantum mechanically interlinked, or "entangled." Devices then encode a 0, 1, or 2 onto one of the photons by performing an operation on it (such as flipping its spin or shifting its phase); since the devices are blind to the initial state of the photon, they change the overall properties of the entangled photon pair without determining its final state. The two photons are recombined and then the interlinked pair travels towards a network of detectors. Two-photon interference creates three different sets of detection possibilities in the Innsbruck setup that reveal the quantum state of the entangled pair and whether the photon was encoded with a 0, 1, or 2. The physics of entanglement has been exploited in numerous recent experiments, to build quantum logic gates (Update 250) and perform an atom-level demonstration of Schrodinger's cat (Update 273), but until now it has never been used for quantum communication---encoding a message at one location and receiving it at another. Furthermore, the same information contained in a typical ASCII character, normally requiring the use of 8 bits, can also be transmitted using only 5 trits. (K. Mattle et al, Physical Review Letters, 17 June 1996. More information and graphics can be found at http://www.uibk.ac.at/c/c7/c704/qo/photon/_qdc) THE CLOSEST EXTRA-SOLAR PLANET yet discovered orbits the star Lalande 21185, only 8.1 light years from Earth. George Gatewood of the University of Pittsburgh observed a telltale wobble in the light coming from the star, indicating the presence of a Jupiter-sized planet circling the star in a Saturn-sized orbit. Gatewood's data, presented at the meeting of the American Astronomical Society in Madison, WI, even hinted at the possibility of other planets in the same solar system. (Washington Post, 12 June.) Also, another planet has been found by Geoff Marcy of San Francisco State and Paul Butler of Berkeley, who announced two new planets in January 1996. Their new find is a Jupiter-sized planet orbiting the star Rho Cancri (40 light years from Earth) at a distance of only 0.1 astronomical units. It completes a "year" in only about two Earth weeks. (Sky & Telescope, July 1996) A MOVIE OF THE CRAB NEBULA provides new details about pulsar dynamics. At the heart of the nebula is a pulsar (the remnant of a 1000-year-old supernova) which casts powerful streams of particles into the surrounding debris-filled medium. The Hubble Space Telescope has recorded a sequence of pictures which show where much of the pulsar's energy goes. One surprise was how quickly the landscape alters: noticeable changes in the region around the pulsar sometimes occurred in a matter of days. A second surprise is that the outward flow of energy is confined largely to two zones: jets shooting out from the poles and wisps of material in the pulsar's equatorial plane. (Science News, 8 June; Science, 7 June.)