528 research outputs found
On the quantum, classical and total amount of correlations in a quantum state
We give an operational definition of the quantum, classical and total amount
of correlations in a bipartite quantum state. We argue that these quantities
can be defined via the amount of work (noise) that is required to erase
(destroy) the correlations: for the total correlation, we have to erase
completely, for the quantum correlation one has to erase until a separable
state is obtained, and the classical correlation is the maximal correlation
left after erasing the quantum correlations.
In particular, we show that the total amount of correlations is equal to the
quantum mutual information, thus providing it with a direct operational
interpretation for the first time. As a byproduct, we obtain a direct,
operational and elementary proof of strong subadditivity of quantum entropy.Comment: 12 pages ReVTeX4, 2 eps figures. v2 has some arguments clarified and
references update
Dynamical coherent-potential approximation approach to excitation spectra in 3d transition metals
First-principles dynamical CPA (Coherent-Potential Approximation) for
electron correlations has been developed further by taking into account
higher-order dynamical corrections with use of the asymptotic approximation.
The theory is applied to the investigations of a systematic change of
excitation spectra in transition metals from Sc to Cu at finite
temperatures. It is shown that the dynamical effects damp main peaks in the
densities of states (DOS) obtained by the local density approximation to the
density functional theory, reduce the band broadening due to thermal spin
fluctuations, create the Mott-Hubbard type bands in the case of fcc Mn and fcc
Fe, and create a small hump corresponding to the `6 eV' satellite in the case
of Co, Ni, and Cu. Calculated DOS explain the X-ray photoelectron spectroscopy
data as well as the bremsstrahlung isochromat spectroscopy data. Moreover, it
is found that screening effects on the exchange energy parameters are
significant for understanding the spectra in magnetic transition metals.Comment: To be published in Phys. Rev.
From extended phase space dynamics to fluid theory
We derive a fluid theory for spin-1/2 particles starting from an extended
kinetic model based on a spin-projected density matrix formalism. The evolution
equation for the spin density is found to contain a pressure-like term. We give
an example where this term is important by looking at a linear mode previously
found in a spin kinetic model.Comment: 4 page
Quantum kinetic theory of the filamentation instability
The quantum electromagnetic dielectric tensor for a multi species plasma is
re-derived from the gauge invariant Wigner-Maxwell system and presented under a
form very similar to the classical one. The resulting expression is then
applied to a quantum kinetic theory of the electromagnetic filamentation
instability. Comparison is made with the quantum fluid theory including a Bohm
pressure term, and with the cold classical plasma result. A number of
analytical expressions are derived for the cutoff wave vector, the largest
growth rate and the most unstable wave vector
Mean Field and the Single Homopolymer
We develop a statistical model for a confined chain molecule based on a
monomer grand canonical ensemble. The molecule is subject to an external
chemical potential, a backbone interaction, and an attractive interaction
between all monomers. Using a Gaussian variable formalism and a mean field
approximation, we analytically derive a minimum principle from which we can
obtain relevant physical quantities, such as the monomer density, and we
explore the limit in which the chain is subject to a tight confinement. Through
a numerical implementation of the minimization process we show how we can
obtain density profiles in three dimensions for arbitraty potentials, and we
test the limits of validity of the theory.Comment: 15 pages, 7 figure
Effect of significant data loss on identifying electric signals that precede rupture by detrended fluctuation analysis in natural time
Electric field variations that appear before rupture have been recently
studied by employing the detrended fluctuation analysis (DFA) as a scaling
method to quantify long-range temporal correlations. These studies revealed
that seismic electric signals (SES) activities exhibit a scale invariant
feature with an exponent over all scales investigated
(around five orders of magnitude). Here, we study what happens upon significant
data loss, which is a question of primary practical importance, and show that
the DFA applied to the natural time representation of the remaining data still
reveals for SES activities an exponent close to 1.0, which markedly exceeds the
exponent found in artificial (man-made) noises. This, in combination with
natural time analysis, enables the identification of a SES activity with
probability 75% even after a significant (70%) data loss. The probability
increases to 90% or larger for 50% data loss.Comment: 12 Pages, 11 Figure
Entropic particle transport: higher order corrections to the Fick-Jacobs diffusion equation
Transport of point-size Brownian particles under the influence of a constant
and uniform force field through a three-dimensional channel with smoothly
varying periodic cross-section is investigated. Here, we employ an asymptotic
analysis in the ratio between the difference of the widest and the most narrow
constriction divided through the period length of the channel geometry. We
demonstrate that the leading order term is equivalent to the Fick-Jacobs
approximation. By use of the higher order corrections to the probability
density we derive an expression for the spatially dependent diffusion
coefficient D(x) which substitutes the constant diffusion coefficient present
in the common Fick-Jacobs equation. In addition, we show that in the diffusion
dominated regime the average transport velocity is obtained as the product of
the zeroth-order Fick-Jacobs result and the expectation value of the spatially
dependent diffusion coefficient . The analytic findings are corroborated
with the precise numerical results of a finite element calculation of the
Smoluchowski diffusive particle dynamics occurring in a reflection symmetric
sinusoidal-shaped channel.Comment: 9 pages, 3 figure
Current and universal scaling in anomalous transport
Anomalous transport in tilted periodic potentials is investigated within the
framework of the fractional Fokker-Planck dynamics and the underlying
continuous time random walk. The analytical solution for the stationary,
anomalous current is obtained in closed form. We derive a universal scaling law
for anomalous diffusion occurring in tilted periodic potentials. This scaling
relation is corroborated with precise numerical studies covering wide parameter
regimes and different shapes for the periodic potential, being either symmetric
or ratchet-like ones
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