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Date: Fri, 16 Mar 2007 11:10:19 -0400
To: eugen@...
Subject: Physics News Update 815
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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 815 March 16, 2007 by Phillip F. Schewe, Ben Stein
www.aip.org/pnu

PHYSICS AND PROGRESS. Why do science? To learn more about the
universe and to improve the material and intellectual conditions of
people. The recently concluded APS March meeting was a great arena
for showcasing new fundamental ideas in physics and also for seeing
how these ideas can be marshaled for producing practical commercial
benefits. Here are three examples:
1. Metamaterials. The architecture of these artificial
nanoscale-engineered materials made of tiny ring-, strip-, and
rod-shaped components serves to enhance the magnetic interaction
between light and matter. This results in the material having a
negative index of refraction and consequentially various novel
optical properties. One practical goal of negative-index optical
research is superlensing, a process in which a thin flat panel of
the metamaterial would be able to image an object at a spatial
resolution better than the wavelength of the illuminating light.
Since metamaterials were first realized in the lab for microwave
light, physicists have been pushing negative-index behavior to
shorter and shorter wavelengths. To bring about a negative-index
condition, the material*s electric permittivity (a measure of a
material's response to an applied electric field) must be negative,
and in some cases also its magnetic permeability (a measure of the
material's response to an applied magnetic field (to read more about
these parameters and early reports of metamaterials, see
http://www.aip.org/pnu/2000/split/pnu476-1.htm). At last week*s APS
meeting Vladimir Shalaev (Purdue University, shalaev@...)
reported a negative-index material operating at a wavelength of 770
nm (at the end of the visible spectrum), the shortest wavelength
observed for a single-negative (negative permittivity) and the same
material (but with a different light polarization) operating at a
wavelength of 815 nm, the shortest wavelength observed for a
double-negative material (both negative permittivity and
permeability). See Shalaev*s review article at Nature Photonics,
January 2007.
2. Graphene, essentially one-atom-thin carbon sheets, were
presented at last year*s meeting by no more than a few groups. Now
there are dozens. The reasons for this are graphene*s adaptable
mechanical and electrical properties and the very unusual behavior
of electrons moving through a graphene landscape: you increase the
electron*s energy but you don*t increase their velocity. It*s as
if
the electrons were acting like slow-moving light waves. Pablo
Jarillo-Herrero (Columbia Univ, pj2168@...) reported the
latest developments in this rapidly moving research area, including
the useful development of graphene ribbons; the resistivity of the
material changes according to the width of the ribbons, meaning that
the semiconducting properties of graphene could be tailored to suit
the application. He also summarized out recent progress in the
field, including the observation of superconducting graphene
transistors (Delft), freely suspended graphene sheets, a
room-temperature Hall effect, and room temperature single-electron
transistors with graphene (Manchester).
3. Light-emitting diodes. Moving from two new topics-metamaterials
and graphene-to a more mature field-the production of light by
combining holes and electrons inside a semiconductor junction-we see
that considerable forward strides are still possible. George
Craford (Lumileds/Philips) described a new record-setting
white-light high-power LED, with an inpu
t current of 350 mA, the
one-square-millimeter device produced light at a rate of 115 lumens
per watt, representing the first time a high-power LED exceeded the
100 Lm/W mark. LEDs, because of their energy efficiency and their
concentration, are already frequently used in traffic lights, brake
lights, and in building lighting. Craford predicted that some LEDs
were to be used in cellphone flashes, in daytime automobile running
lights, and (later this year) for auto headlights.

WIRELESS TRANSMISSION OF QUANTUM CODE over a distance of 144
kilometers (89 miles) between two Canary Islands has been
demonstrated by a team of researchers in Europe. At the APS March
Meeting, Anton Zeilinger of the University of Vienna
(anton.zeilinger@...) described how he and his colleagues
transmitted single photons from an astronomical observatory in La
Palma Island to another one in Tenerife. The transmitted photons'
polarization states (representing 0s and 1s) formed the basis of a
"quantum key," a stream of information that could be used to
decipher a longer encrypted message. The researchers used single
photons because they are more secure than groups of photons, from
which an eavesdropper could pluck information about the key. To
detect potential eavesdroppers even better, the researchers
entangled the outgoing particles of light with photons kept at the
transmitting station. They used astronomy stations because their
telescopes are sensitive enough to detect individual photons. The
data transmission rate was low, only 178 photons in 75 seconds, but
the photons are able to travel longer distances in free space
(potentially thousands of kilometers or more) than they are in fiber
optic cables (100 km) before they become undetectable. In a
proposed experiment to be coordinated by the European Space Agency
(ESA, which operates the Tenerife telescope and which participated
in the Canary Islands experiment) the International Space Station
can transmit entangled key to two earthbound stations separated by
distances ten times greater or more. (For a preprint, see Ursin et
al., quant-ph/0607182)

***********
PHYSICS NEWS UPDATE is a digest of physics news items arising
from physics meetings, physics journals, newspapers and
magazines, and other news sources. It is provided free of charge
as a way of broadly disseminating information about physics and
physicists. For that reason, you are free to post it, if you like,
where others can read it, providing only that you credit AIP.
Physics News Update appears approximately once a week.

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