Physics Colloquium on Thursday

[Jerri McLemore]

PHYSICS COLLOQUIUM


Dr. Nikolai Prokofiev
University of Massachusetts

"Spin Bath Decoherence in Magnets and Superconductors"


Abstract:

                The quantum dynamics of mesoscopic or macroscopic systems is
always complicated by their coupling to many "environmental" modes.  I will
present arguments that at low T these environmental effects are dominated by
localized modes, such as nuclear and paramagnetic spins, and defects (which
also dominated the entropy and specific heat).  This environment, at low
energies, maps onto a "spin bath" model.  This contrasts with "oscillator
bath" models which describe de-localized environmental modes such as
electrons, phonons, photons, magnons, etc.  For example, the spin bath
environment causes decoherence even in the T<< 1mK regime.  Control of this
decoherenceis is crucial in the effort to construct "qubits" for quantum
computers.
                I will show how the mapping to spin bath models is made, and
then discuss two examples in detail, namely, nanomagnets and SQUIDS, coupled
to nuclear and paramagnetic spin environments.  Finally, I will review
recent experimental work on tunneling in magnetic macromolecules, where the
role of the nuclear spin bath in controlling the tunneling is very clear; I
will also discuss other magnetic systems in the quantum regime, and the
influence of nuclear and paramagnetic spins on flux dynamics in SQUIDs.


Thursday, January 24, 2002
4:00 p.m., Room 202
Engineering/Physics Building

Department of Physics
Texas A&M University

Presentation of an engraved pen to this week's speaker has been made
possible by John Wiley Publishing Company.

Coffee, hot tea, and cookies will be served in Room 202, 3:45 p.m.