4,333 research outputs found
Two interacting atoms in a cavity: exact solutions, entanglement and decoherence
We address the problem of two interacting atoms of different species inside a
cavity and find the explicit solutions of the corresponding eigenvalues and
eigenfunctions using a new invariant. This model encompasses various commonly
used models. By way of example we obtain closed expressions for concurrence and
purity as a function of time for the case where the cavity is prepared in a
number state. We discuss the behaviour of these quantities and and their
relative behaviour in the concurrence-purity plane.Comment: 10 pages, 3 figure
Decoherence at constant excitation
We present a simple exactly solvable extension of of the Jaynes-Cummings
model by adding dissipation. This is done such that the total number of
excitations is conserved. The Liouville operator in the resulting master
equation can be reduced to blocks of matrices
A random matrix approach to decoherence
In order to analyze the effect of chaos or order on the rate of decoherence
in a subsystem, we aim to distinguish effects of the two types of dynamics by
choosing initial states as random product states from two factor spaces
representing two subsystems. We introduce a random matrix model that permits to
vary the coupling strength between the subsystems. The case of strong coupling
is analyzed in detail, and we find no significant differences except for very
low-dimensional spaces.Comment: 11 pages, 5 eps-figure
Preventing adolescents’ externalizing and internalizing symptoms : effects of the Penn Resiliency Program
This study reports secondary outcome analyses from a past study of the Penn Resiliency
Program (PRP), a cognitive-behavioral depression prevention program for middle-school
aged children. Middle school students (N = 697) were randomly assigned to PRP, PEP
(an alternate intervention), or control conditions. Gillham et al., (2007) reported analyses
examining PRP’s effects on average and clinical levels of depression symptoms. We
examine PRP’s effects on parent-, teacher-, and self-reports of adolescents’ externalizing
and broader internalizing (depression/anxiety, somatic complaints, and social
withdrawal) symptoms over three years of follow-up. Relative to no intervention control,
PRP reduced parent-reports of adolescents’ internalizing symptoms beginning at the first
assessment after the intervention and persisting for most of the follow-up assessments.
PRP also reduced parent-reported conduct problems relative to no-intervention. There
was no evidence that the PRP program produced an effect on teacher- or self-report of
adolescents’ symptoms. Overall, PRP did not reduce symptoms relative to the alternate
intervention, although there is a suggestion of a delayed effect for conduct problems.
These findings are discussed with attention to developmental trajectories and the
importance of interventions that address common risk factors for diverse forms of
negative outcomes.peer-reviewe
Spectral sum rules and finite volume partition function in gauge theories with real and pseudoreal fermions
Based on the chiral symmetry breaking pattern and the corresponding
low-energy effective lagrangian, we determine the fermion mass dependence of
the partition function and derive sum rules for eigenvalues of the QCD Dirac
operator in finite Euclidean volume. Results are given for and for
Yang-Mills theory coupled to several light adjoint Majorana fermions. They
coincide with those derived earlier in the framework of random matrix theory.Comment: 22p., SUNY-NTG-94/18, TPI-MINN-94/10-
Fidelity amplitude of the scattering matrix in microwave cavities
The concept of fidelity decay is discussed from the point of view of the
scattering matrix, and the scattering fidelity is introduced as the parametric
cross-correlation of a given S-matrix element, taken in the time domain,
normalized by the corresponding autocorrelation function. We show that for
chaotic systems, this quantity represents the usual fidelity amplitude, if
appropriate ensemble and/or energy averages are taken. We present a microwave
experiment where the scattering fidelity is measured for an ensemble of chaotic
systems. The results are in excellent agreement with random matrix theory for
the standard fidelity amplitude. The only parameter, namely the perturbation
strength could be determined independently from level dynamics of the system,
thus providing a parameter free agreement between theory and experiment
Relativistic echo dynamics and the stability of a beam of Landau electrons
We extend the concepts of echo dynamics and fidelity decay to relativistic
quantum mechanics, specifically in the context of Klein-Gordon and Dirac
equations under external electromagnetic fields. In both cases we define
similar expressions for the fidelity amplitude under perturbations of these
fields, and a covariant version of the echo operator. Transformation properties
under the Lorentz group are established. An alternate expression for fidelity
is given in the Dirac case in terms of a 4-current. As an application we study
a beam of Landau electrons perturbed by field inhomogeneities.Comment: 8 pages, no figure
Nonperiodic echoes from mushroom billiard hats
Mushroom billiards have the remarkable property to show one or more clear cut
integrable islands in one or several chaotic seas, without any fractal
boundaries. The islands correspond to orbits confined to the hats of the
mushrooms, which they share with the chaotic orbits. It is thus interesting to
ask how long a chaotic orbit will remain in the hat before returning to the
stem. This question is equivalent to the inquiry about delay times for
scattering from the hat of the mushroom into an opening where the stem should
be. For fixed angular momentum we find that no more than three different delay
times are possible. This induces striking nonperiodic structures in the delay
times that may be of importance for mesoscopic devices and should be accessible
to microwave experiments.Comment: Submitted to Phys. Rev. E without the appendi
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