Physics News Update 662 (fwd)

[Jim Choate]

---------- Forwarded message ----------
Date: Tue, 18 Nov 2003 11:34:46 -0500
From: physnews at aip.org
To: ravage at SSZ.COM
Subject: Physics News Update 662

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 662 November 18, 2003   by Phillip F. Schewe, Ben Stein, and
James Riordon

A LIQUID WALL IN A FUSION ENERGY DEVICE has improved the performance
[SSZ: text deleted]

ELECTRON SPINS CAN CONTROL NUCLEAR SPINS in a semiconductor when
trapped in a very confined space, a recent experimental development
which calls upon laser science, solid-state physics, and nuclear
magnetic resonance.  David Awschalom and his colleagues at the Center for
Spintronics and Quantum Computation at UC Santa Barbara begin by
lithographically creating a quantum well, an extremely thin,
practically two-dimensional region inside a semiconductor
capable of trapping electrons. First, a laser pulse injects
polarized electrons (their spins have a definite orientation
determined by the laser's polarization) into the well.  Once in the
well, the tiny disk of electrons (with a radius of about 20 microns
but a thickness of only 20 nm) can be controllably moved along one
axis, much as an abacus bead can be slid along a wire, by simply
changing a voltage.  In this case, the disk can be positioned with
nm-accuracy.  The nuclei of atoms residing within the thin
volume occupied by the spin-polarized
electrons will in turn be polarized; that is, the spin of these
nuclei will tend to align themselves with the spin of the
electrons.  The result is an extremely thin region---equivalent to
the thickness of several tens of atoms--- of polarized nuclei
which can be precisely positioned by changing a single voltage.
These thin sheets of nuclear polarization could constitute the basic
elements of an information storage device in which nuclear spin
determines the logical state of the system.  One may ask, why not
take out the "middle man" and just use the electron spin to encode
information?  The answer: nuclear spins have a weaker interaction
with the surrounding environment than electron spins.  While harder
to flip, once oriented, nuclear spins preserve their state longer
than do electrons.  One may also wonder, why not just use some large
magnet to orient the nuclear spins?  Why use electrons as
intermediaries?  The answer: all-electronic control of spin is
desirable because electric fields are so much easier to control and
create on a small scale than magnetic fields.  They are scalable and
easy to implement, while it is notoriously hard to produce large and
localized magnetic fields.  In addition, all of our current
integrated circuit technology is based on charge and electric field;
it would certainly be helpful to manipulate spin using "knobs" which
are well developed and familiar to engineers.  Awschalom
(awsch at physics.ucsb.edu, 805-893-2121) believes this current result
is the first step toward the establishment of an all-electrical
manipulation of countable numbers of nuclear spins.(Poggio et al.,
Physical Review Letters, 14 November 2003)


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