PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 698 August 26, 2004
by Phillip F. Schewe, Ben Stein
        
THE WORLD'S SMALLEST ATOMIC CLOCK, about the size of a rice grain, is built
around a microcell about 1 cubic mm in volume filled with cesium atoms.  It
draws only about 30 mA of current from a 2.5 V battery.  Atomic clocks are
the best timekeepers because they are able to convert the high-precision
information contained in the light emitted by alkali atoms (the light
emerging from an atomic transition from one energy level to another can be
measured to an uncertainty of better than a part in a billion) into a
usable standard for defining the second.  The new miniature clock has a
precision of 3.5 x 10^-10.  What this means is that events can be timed
with an uncertainty of about one part in 3 billion. Scientists at NIST in
Boulder, Colorado make atomic clocks that are far more precise---the F-1
clock is good to about one part in 10 trillion---but this requires a huge
table-top's worth of equipment. The mini version being reported now should
eventually reach a stability of about 10^-11, some 10,000 times better than
any quartz oscillator clock of equivalent size and power.  How will this
new cheap, tiny, low-power, high-precision MEMS clock be used?  In
satellites, GPS receivers, networked computer CPU's, possibly in cell
phones.  (Knappe et al., Applied Physics Letters, 30 August 2004; contact
John Kitching, kitching{at}boulder.nist.gov, 303-497-3328; for an explanation
of precision and accuracy, see
www.boulder.nist.gov/timefreq/general/about.html)

OPTICAL FUNNEL FOR FOCUSING COLD ATOMS. A new experiment at the Tokyo
Institute of Technology uses evanescent light to focus cold atoms and
output as a beam. Evanescent light is the faint optical field (a sort of
aura of light stuck on a material) that is found on the material surface
when a laser beam reflects away from the material via "total internal
reflection." In this case, the focusing effect occurs when a hollow
laser beam moving upwards splays outward around a funnel-shaped piece of
glass. The light, shone downward and covering the inner edge of this
funnel, helps to repel and cool a blob of atoms held and chilled in a
magneto-optical trap (MOT) and falling slightly under the force of gravity.
 Evanescent light has been used before to guide atoms through a hollow
optical fiber (see http://www.aip.org/pnu/1996/split/pnu272-2.htm), but in
the Tokyo work there are new features: high flux intensity, low
temperature, and small beam diameter.  The funnel focuses an atom swarm
about 2 mm wide is forced to collimate down to the size of the funnel's
exit hole, which in the experiment was 200 microns, for a net focusing
factor of 100 (see figure at www.aip.org/png). Furthermore, a micron-sized
hole is now being tested, which should result in a focusing factor of a
million, and a beam flux intensity of some 10^15 atoms/cm^2-s. Akifumi
Takamiazwa
(Akifumi.Takamizawa{at}physik.uni-muenchen.de) says that he and his colleagues
hope to make a nanometer-sized funnel as small as atomic de Broglie
wavelength and use it eventually for single-atom manipulation, perhaps for
processes in which one atom can transfer one bit of information.
(Takamizawa et al., Applied Physics Letters, 6 September 2004; see
http://uuu.ae.titech.ac.jp/research-e.html and
http://www.coe21-pni.titech.ac.jp/eng/task/index.htm)

SUPERPROTONIC TRANSITIONS.  Electrons are the charge carriers in most
electronic transactions.  Sometimes, in semiconductors, holes, the moving
voids recently vacated by an electron, constitute a usable current flow. 
But positive ions can also act as an important current.  Lead-acid
batteries in cars are a prominent application of this principle.  A
particularly interesting phenomenon in this regard is the
"superprotonic" transition, an effect discovered in the 1980s by
Russian scientists, in which the proton conductivity jumps by several
orders of magnitude at a certain temperature, when a structural
rearrangement of some of the molecular oxyamion groups (such as SO4)
occurs.  Sossina M. Haile and her colleagues at Caltech
(smhaile{at}caltech.edu, 626-395-2958) have performed new experiments which
have expanded the roster of superprotonic materials, or cleared up past
mysteries.  For example, they have cleared up any doubt that the solid-form
acid CsH2PO4, whose chemistry and conducting properties are especially
promising as a candidate for the electrolyte in fuel cells, can undergo the
superprotonic transition.  The new results were reported at last month's
meeting of the American Crystallographic Association in Chicago
(http://www.hwi.buffalo.edu/ACA/; see also http://addis.caltech.edu/)

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