PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 722 March 3, 2005
by Phillip F. Schewe, Ben Stein
        
240 ELECTRONS SET IN MOTION.  A soccerball-shaped carbon-60 molecule,
possessing a mobile team of up to about 240 valence electrons holding the
structure together, is sort of halfway between being a molecule and a
solid.   To explore how all those electrons can move as an ensemble, a team
of scientists working at the Advanced Light Source synchrotron radiation
lab in Berkeley, turned the C-60 molecules into a beam (by first ionizing
them) and then shot ultraviolet photons at them.  When a photon absorbed,
the energy can be converted into a collective movement of the electrons
referred to as a plasmon.  Previously a 20-electron-volt "surface
plasmon" was observed: the absorption of the UV energy resulted in a
systematic oscillation of the ensemble of electrons visualized as a thin
sphere of electric charge.  Now a new experiment has found evidence of a
second resonance at an energy of 40 eV.  This second type of collective
excitation is considered a "volume plasmon" since the shape of
the collective electron ensemble is thought to be oscillating with respect
to the center of the molecule (see figure at
http://www.aip.org/png/2005/230.htm).  The collaboration consists of
physicists from the University of Nevada, Reno (Ronald Phaneuf,
775-784-6818, phaneuf{at}unr.
edu), Lawrence Berkeley National Lab, Justus-Liebig-University (Giessen,
Germany), and the Max Planck Institute (Dresden).  (Scully et al., Physical
Review Letters, 18 February 2005)

FIRST EVIDENCE FOR ENTANGLEMENT OF THREE MACROSCOPIC OBJECTS has been seen
in a superconducting circuit built at the University of Maryland.  By
examining an electrical circuit operating at temperatures near absolute
zero, the researchers have found new evidence that the laws of quantum
mechanics apply not just to microscopic particles such as atoms and
electrons, but also to large electronic devices called superconducting
quantum bits (qubits). While researchers have previously created
superconducting qubits, and other groups have entangled two macroscopic
objects (Update 558), this research is the first to observe the quantum
interaction of three macroscopic components: a niobium inductor-capacitor
(LC) circuit plus a pair of Josephson junctions, each a sandwich of two
superconductors separated by an insulator.  Remarkably, all three
macroscopic devices seem to act, when cold enough, like huge atoms.  The LC
circuit coupled the Josephson junctions in such a way as to transfer
quantized oscillations of current in one junction to the other junction. 
The LC circuit was more than a simple connector; its condition depended
upon the two Josephson junctions in a way defined by the laws of quantum
mechanics.  The researchers obtained evidence of the entanglement
indirectly, through the use of microwave pulses that probed the Josephson
junctions; future experiments will seek to directly control the junctions
and obtain evidence more directly. Superconducting circuits such as this
one provide a promising route towards a practical quantum computer, which
would require the entanglement of many qubits. Scaling up superconducting
devices to many-qubit systems should be possible once single
superconducting qubits are perfected, according to team member Frederick
Strauch, (now at NIST, 301-975-5159, Frederick.Strauch{at}nist.gov). The
challenge will be to fabricate sufficiently high-quality circuits so that
the superconducting qubits achieve the very low noise levels necessary for
quantum computing. (Xu et al., Physical Review Letters, 21 January 2005)
                        
X-RAY THUNDERBOLT.  Scientists have long suspected that lightning might
generate x rays.  However, until recently the observation of such x-rays
has remained elusive, largely owing to the unpredictable nature of
lightning.  In the last few years a series of experiments by Joseph Dwyer
and his colleagues at the Florida Institute of Technology and the
University of Florida has shown that lightning indeed emits large bursts of
x rays with energies up to about 250 keV (about twice that of a chest x
ray).  These x rays are mostly produced not by the bright return strokes,
but by the leaders that precede the stroke, as they propagate from the
cloud to the ground. Now, Dwyer and his colleagues have discovered that
these bursts of x rays are produced at the precise moment that the
lightning steps forward along its jagged path.  For unknown reasons,
lightning does not travel to the ground in a continuous manner, but instead
traverses the distance in a series of discrete steps.  It is this stepping
process that gives lightning its jagged, sometimes forked, appearance, and
Dwyer has now shown that this same stepping process also makes x rays.  The
x rays are likely produced by strong electric fields that accelerate
electrons to close to the speed of light.  These so-called runaway
electrons collide with air producing bremsstrahlung ("braking
radiation" in German) x-rays. Dwyer says that higher energy gamma rays
are also emitted sometimes, but that these seem to come from the
thunderstorm cloud itself and not from the lightning stroke.  (Dwyer et
al., Geophysical Review Letters, 16 January 2005.)

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