1,667 research outputs found
Probability assignment in a quantum statistical model
The evolution of a quantum system, appropriate to describe nano-magnets, can
be mapped on a Markov process, continuous in . The mapping implies a
probability assignment that can be used to study the probability density (PDF)
of the magnetization. This procedure is not the common way to assign
probabilities, usually an assignment that is compatible with the von Neumann
entropy is made. Making these two assignments for the same system and comparing
both PDFs, we see that they differ numerically. In other words the assignments
lead to different PDFs for the same observable within the same model for the
dynamics of the system. Using the maximum entropy principle we show that the
assignment resulting from the mapping on the Markov process makes less
assumptions than the other one. Using a stochastic queue model that can be
mapped on a quantum statistical model, we control both assignments on
compatibility with the Gibbs procedure for systems in thermal equilibrium and
argue that the assignment resulting from the mapping on the Markov process
satisfies the compatibility requirements.Comment: 8 pages, 2 eps figures, presented at the 26-th International Workshop
on Bayesian Inference and Maximum Entropy Methods in Science and Engineering,
200
Comment on: rotational properties of trapped bosons
Based on the Hellman-Feynman theorem it is shown that the average square
radius of a cloud of interacting bosons in a parabolic well can be derived from
their free energy. As an application, the temperature dependence of the moment
of inertia of non-interacting bosons in a parabolic trap is determined as a
function of the number of bosons. Well below the critical condensation
temperature, the Bose-Einstein statistics are found to substantially reduce the
moment of inertia of this system, as compared to a gas of ``distinguishable''
particles in a parabolic well.Comment: Herewith we repost our paper cond-mat/9611090 (1996). It was
published in Phys. Rev. A 55, 2453 (March 1997), three years before
cond-mat/0003471 (2000) by Schneider and Wallis. Reposted by
[email protected]
The center-of-mass response of confined systems
For confined systems of identical particles, either bosons or fermions, we
argue that the parabolic nature of the confinement potential is a prerequisite
for the non-dissipative character of the center of mass response to a uniform
probe. For an excitation in a parabolic confining potential, the half width of
the density response function depends nevertheless quantitatively on properties
of the internal degrees of freedom, as is illustrated here for an ideal
confined gas of identical particles with harmonic interparticle interactions.Comment: 4 pages REVTEX; accepted as Brief Communication in Phys. Rev.
Electronic Raman scattering in Tl2Ba2CuO6+x: symmetry of the order parameter, oxygen doping effects, and normal state scattering
Single crystals of the optimally doped, moderately and strongly overdoped
high temperature superconductor Tl2Ba2CuO6+x (Tl-2201) with Tc=80, 56 and 30K,
respectively, have been investigated by polarized Raman scattering. By taking
the peak position of the B_1g component of electronic Raman scattering as
2Delta_0 we found that the reduced gap value (2Delta_0/k_BT_c) strongly
decreases with increasing doping. The behavior of the low frequency scattering
for the B_1g and B_2g scattering components is similar for optimally doped and
overdoped crystals and can be described by a w^3 - and w -law, respectively,
which is consistent with a d-wave symmetry of the order parameter. In contrast
to the optimally doped Tl-2201 in both, moderately and strongly overdoped
Tl-2201, the relative (compared to the B_1g) intensity of the A_1g scattering
component is suppressed. We suggest that the van Hove singularity is
responsible for the observed changes of Raman intensity and reduced gap value
with doping. Electronic Raman scattering in the normal state is discussed in
the context of the scattering from impurities and compared to the existing
infrared data. The scattering rate evaluated from the Raman measurements is
smaller for the overdoped samples, compared to the moderately overdoped
samples.Comment: 7 pages, 7 figure
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