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.)
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