756 research outputs found
Surface-induced heating of cold polar molecules
We study the rotational and vibrational heating of diatomic molecules placed
near a surface at finite temperature on the basis of macroscopic quantum
electrodynamics. The internal molecular evolution is governed by transition
rates that depend on both temperature and position. Analytical and numerical
methods are used to investigate the heating of several relevant molecules near
various surfaces. We determine the critical distances at which the surface
itself becomes the dominant source of heating and we investigate the transition
between the long-range and short-range behaviour of the heating rates. A simple
formula is presented that can be used to estimate the surface-induced heating
rates of other molecules of interest. We also consider how the heating depends
on the thickness and composition of the surface.Comment: 17 pages, 7 figure
Ground-state van der Waals forces in planar multilayer magnetodielectrics
Within the frame of lowest-order perturbation theory, the van der Waals
potential of a ground-state atom placed within an arbitrary dispersing and
absorbing magnetodielectric multilayer system is given. Examples of an atom
situated in front of a magnetodielectric plate or between two such plates are
studied in detail. Special emphasis is placed on the competing attractive and
repulsive force components associated with the electric and magnetic matter
properties, respectively, and conditions for the formation of repulsive
potential walls are given. Both numerical and analytical results are presented.Comment: 16 pages, 8 figures, minor correction
Casimir force on amplifying bodies
Based on a unified approach to macroscopic QED that allows for the inclusion
of amplification in a limited space and frequency range, we study the Casimir
force as a Lorentz force on an arbitrary partially amplifying system of
linearly locally responding (isotropic) magnetoelectric bodies. We demonstrate
that the force on a weakly polarisable/magnetisable amplifying object in the
presence of a purely absorbing environment can be expressed as a sum over the
Casimir--Polder forces on the excited atoms inside the body. As an example, the
resonant force between a plate consisting of a dilute gas of excited atoms and
a perfect mirror is calculated
Interatomic van der Waals potential in the presence of a magneto-electric sphere
On the basis of a general formula obtained earlier via fourth-order
erturbation theory within the framework of macroscopic quantum electrodynamics,
the van der Waals potential between two neutral, unpolarized, ground-state
atoms in the presence of a homogeneous, dispersing and absorbing
magnetoelectric sphere is studied. When the radius of the sphere becomes
sufficiently large, the result asymptotically agrees with that for two atoms
near a planar interface. In the opposite limit of a very small sphere, the
sphere can effectively be regarded as being a third ground-state atom, and the
nonadditive three-atom van der Waals potential is recovered. To illustrate the
effect of a sphere of arbitrary radius, numerical results are presented for the
triangular arrangement where the atoms are at equidistance from the sphere, and
for the linear arrangement where the atoms and the sphere are aligned along a
straight line. As demonstrated, the enhancement or reduction of the interaction
potential in the presence of purely electric or magnetic spheres can be
physically understood in terms of image charges.Comment: 13 pages, 7 figure
Thermopower of a Kondo-correlated quantum dot
The thermopower of a Kondo-correlated gate-defined quantum dot is studied
using a current heating technique. In the presence of spin correlations the
thermopower shows a clear deviation from the semiclassical Mott relation
between thermopower and conductivity. The strong thermopower signal indicates a
significant asymmetry in the spectral density of states of the Kondo resonance
with respect to the Fermi energies of the reservoirs. The observed behavior can
be explained within the framework of an Anderson-impurity model.
Keywords: Thermoelectric and thermomagnetic effects, Coulomb blockade, single
electron tunneling, Kondo-effect
PACS Numbers: 72.20.Pa, 73.23.HkComment: 4 pages, 4 figures, revised version, changed figure
Sequential and co-tunneling behavior in the temperature-dependent thermopower of few-electron quantum dots
We have studied the temperature dependent thermopower of gate-defined,
lateral quantum dots in the Coulomb blockade regime using an electron heating
technique. The line shape of the thermopower oscillations depends strongly on
the contributing tunneling processes. Between 1.5 K and 40 mK a crossover from
a pure sawtooth- to an intermitted sawtooth-like line shape is observed. The
latter is attributed to the increasing dominance of cotunneling processes in
the Coulomb blockade regime at low temperatures.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
Laughlin liquid - Wigner solid transition at high density in wide quantum wells
Assuming that the phase transition between the Wigner solid and the Laughlin
liquid is first-order, we compare ground-state energies to find features of the
phase diagram at fixed . Rather than use the Coulomb interaction, we
calculate the effective interaction in a square quantum well, and fit the
results to a model interaction with length parameter roughly
proportional to the width of the well. We find a transition to the Wigner solid
phase at high density in very wide wells, driven by the softening of the
interaction at short distances, as well as the more well-known transition to
the Wigner solid at low density, driven by Landau-level mixing.Comment: RevTeX 3.0, 3 Postscript figures appended in uuencoded forma
Proteome coverage prediction with infinite Markov models
Motivation: Liquid chromatography tandem mass spectrometry (LC-MS/MS) is the predominant method to comprehensively characterize complex protein mixtures such as samples from prefractionated or complete proteomes. In order to maximize proteome coverage for the studied sample, i.e. identify as many traceable proteins as possible, LC-MS/MS experiments are typically repeated extensively and the results combined. Proteome coverage prediction is the task of estimating the number of peptide discoveries of future LC-MS/MS experiments. Proteome coverage prediction is important to enhance the design of efficient proteomics studies. To date, there does not exist any method to reliably estimate the increase of proteome coverage at an early stage
Casimir-Polder forces: A non-perturbative approach
Within the frame of macroscopic QED in linear, causal media, we study the
radiation force of Casimir-Polder type acting on an atom which is positioned
near dispersing and absorbing magnetodielectric bodies and initially prepared
in an arbitrary electronic state. It is shown that minimal and multipolar
coupling lead to essentially the same lowest-order perturbative result for the
force acting on an atom in an energy eigenstate. To go beyond perturbation
theory, the calculations are based on the exact center-of-mass equation of
motion. For a nondriven atom in the weak-coupling regime, the force as a
function of time is a superposition of force components that are related to the
electronic density-matrix elements at a chosen time. Even the force component
associated with the ground state is not derivable from a potential in the
ususal way, because of the position dependence of the atomic polarizability.
Further, when the atom is initially prepared in a coherent superposition of
energy eigenstates, then temporally oscillating force components are observed,
which are due to the interaction of the atom with both electric and magnetic
fields.Comment: 23 pages, 3 figures, additional misprints correcte
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