Plenarvorträge - DPG-Tagungen

Dynamik und Statistische Physik Freitag
DY 50.3 Fr 11:00 H2
Exact decoherence to pointer states in free open quantum systems
is universal — •Jens Eisert — Institut für Physik, Universität
Potsdam, Am Neuen Palais 10, D-14469 Potsdam
In this talk it is shown that exact decoherence to minimal uncertainty
Gaussian pointer states is generic for free quantum particles coupled to
a heat bath. More specifically, the paper is concerned with damped free
particles linearly coupled to a heat bath at arbitrary temperature, with
arbitrary coupling strength and spectral densities covering the ohmic,
subohmic, and supraohmic regime. Then it is true that there exists a time
tc such that for times t > tc the state can always be exactly represented as
a mixture (convex combination) of particular minimal uncertainty Gaussian
states, regardless of the initial state. This exact ‘localisation’ is hence
not only a feature of the high temperature and weak damping limit, but
rather a generic property of damped free particles.
DY 50.4 Fr 11:15 H2
Semiclassical form factor for spectral and matrix element fluctuations
— •Marko Turek 1 , Dominique Spehner 2 , Sebastian
Müller 2 , and Klaus Richter 1 — 1 Institut für theoretische Physik,
Universität Regensburg, D-93040 Regensburg — 2 Fachbereich Physik,
Universität Duisburg-Essen, D-45117 Essen
We present a semiclassical analysis of the spectral form factor in hyperbolic
chaotic systems that includes classical action correlations. Our
calculation is based on recent developments [1] which extend the original
configuration space approach [2] towards a phase space approach but are
still restricted to two-dimensional systems. Here we present a calculation
of the spectral form factor for systems with more than two degrees of
freedom showing that the leading contributions do not depend on the
dimensionality of the system. Furthermore we consider a generalization
towards a form factor for matrix element fluctuations.
[1] D. Spehner, J. Phys. A: Math. Gen. 36, 7269 (2003); M. Turek
and K. Richter, J. Phys. A: Math. Gen. 36, L455 (2003); S. Müller,
Eur. Phys. Jour. B 34, 305 (2003)
[2] M. Sieber and K. Richter, Physica Scripta T90, 128 (2001)
DY 50.5 Fr 11:30 H2
Is the Quantum Dynamics of an Open Quantum System always
Linear? — •Peter Hänggi, Peter Talkner, and Karen M.
Fonseca-Romero — Institut für Physik, Universität Augsburg, Universitätsstr.
1, D-86135 AUGSBURG
We study the influence of the preparation of an open quantum systerm
on its reduced time evolution. In contrast to the widely studied case of
an initial preparation where the total density matrix factorizes into a
product of system density matrix and bath density matrix the time evo-
DY 51 Polymers and Colloids
lution generally is no longer governed by a linear map. Put differently,
the evolution is truely nonlinear and cannot be cast into the form of a
linear map plus a term that is independent of the initial denisty matrix of
the open system (no affine time evolution). As a consequence, the inhomogeneity
that emerges in formally exact generalized master equatins is
in fact a nonlinear term that vanishes only for a factorizing initial state.
The general results are elucidated with the example of two interacting
spins prepared in thermal equilibrium with one spin subjected to external
fields.
DY 50.6 Fr 11:45 H2
Statistical Relaxation Behaviour in closed Quantum Systems
— •Jochen Gemmer — Institut für Theoretische Physik I, Universität
Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart
It is known that quantum systems like atoms, spins etc. tend to decay
from exited states to their ground states in a purely statistical manner,
i.e. by an exponential decay process. This behaviour is explained
by famous concepts like Fermi’s Golden Rule, Weisskopf-Wigner Theory
or Quantum-Masterequations. All those concepts, however, rely on
additional assumptions or infinitely large environments.
We present a model of a spin coupled to a finite environment, in which
the spin shows a statistical relaxation behaviour, while the dynamics of
the full system are treated strictly according to the Schrödinger equation.
DY 50.7 Fr 12:00 H2
Quantum Reversibility: Is there an Echo? — •Moritz Hiller 1 ,
Tsampikos Kottos 1 , Doron Cohen 2 , and Theo Geisel 1 — 1 Max-
Planck-Institut für Strömungsforschung und Fakultät Physik der Universität
Göttingen, Bunsenstraße 10, 37073 Göttingen, Germany —
2 Department of Physics, Ben-Gurion University, Beer-Sheva 84105, Is-
rael
We study the possibility to undo the quantum mechanical evolution in
a time reversal experiment [1]. The naive expectation, as reflected in the
common terminology (“Loschmidt echo”), is that maximum compensation
results if the reversed dynamics extends to the same time as the
forward evolution. We challenge this belief, and demonstrate that the
time tr for maximum return probability is in general shorter. We find
that tr depends on λ = εevol/εprep, being the ratio of the error in setting
the parameters (fields) for the time reversed evolution to the perturbation
which is involved in the preparation process. Our results should be
observable in spin-echo experiments where the dynamical irreversibility
of quantum phases is measured.
[1] M.Hiller, T.Kottos, D.Cohen and T.Geisel, quant-ph/0308112
Zeit: Freitag 10:45–12:30 Raum: H3
DY 51.1 Fr 10:45 H3
Field-theoretic description of semiflexible polymers — •Semjon
Stepanow — Universität Halle, Fachbereich Physik, 06099 Halle
In using the connection between the Kratky-Porod model of a semiflexible
polymer and the quantum rigid rotator in an external homogeneous
field, and its treatment in the framework of the quantum mechanical
propagator method we have shown that most relations for flexible
polymers can be generalized to semiflexible ones, if one replaces
the Edwards-de Gennes propagator, 1/(k 2 /3 + p), through the matrix
P(k, p) = (I + ikDM) −1 D, where the infinite rank matrices D and M
are related to the spectrum of the quantum rigid rotator.
Within this framework we have expressed the distribution function for
a semiflexible polymer in half space in terms of the end-to-end distribution
function of free semiflexible polymer. We present results of the
study of the behaviour of a semiflexible polymer in the vicinity of a wall,
and of adsorption of a semiflexible polymer in weak interface and surface
potentials.
DY 51.2 Fr 11:00 H3
Motion of colloidal crystals and fluids in homogeneous electric
fields — •Thomas Palberg and Martin Medebach — Johannes
Gutenberg Universität Mainz, Institut f. Physik, KOMET 336,
Staudinger Weg 7, D - 55128 Mainz
A charged particle subjected to an electric field E will acquire a constant
velocity v due to the balance of accelerating electrostatic forces
and friction forces. Within the standard electrokinetic model the mobility
u = v/E depends on the surface or Zeta-potential and thus on the
particle charge. In this contribution we present a super-heterodyne reference
beam Doppler Velocimetry experiment to accurately measure the
mobility u under conditions of strong particle interaction. Integral flow
measurements are used for fluid samples, while spatially resolved measurements
are needed for crystalline suspensions. The rich flow scenario
observed there is presented in some detail. A prescription to determine
the true mobility in the presence of non-parabolic flow profiles (e.g. partial
plug-flow or shear banding)is proposed. The mobility is observed to
coincide with expectations based on the standard electrokinetic model
and a numerically determined effective renormalised charge only in the
crystalline state. For fluid order or isolated spheres significant deviations
towards lower values are observed.