925 research outputs found
A link between the maximum entropy approach and the variational entropy form
The maximum entropy approach operating with quite general entropy measure and
constraint is considered. It is demonstrated that for a conditional or
parametrized probability distribution there is a "universal"
relation among the entropy rate and the functions appearing in the constraint.
It is shown that the recently proposed variational formulation of the entropic
functional can be obtained as a consequence of this relation, that is from the
maximum entropy principle. This resolves certain puzzling points appeared in
the variational approach
Bayesian Analysis of Inflation: Parameter Estimation for Single Field Models
Future astrophysical datasets promise to strengthen constraints on models of
inflation, and extracting these constraints requires methods and tools
commensurate with the quality of the data. In this paper we describe ModeCode,
a new, publicly available code that computes the primordial scalar and tensor
power spectra for single field inflationary models. ModeCode solves the
inflationary mode equations numerically, avoiding the slow roll approximation.
It is interfaced with CAMB and CosmoMC to compute cosmic microwave background
angular power spectra and perform likelihood analysis and parameter estimation.
ModeCode is easily extendable to additional models of inflation, and future
updates will include Bayesian model comparison. Errors from ModeCode contribute
negligibly to the error budget for analyses of data from Planck or other next
generation experiments. We constrain representative single field models (phi^n
with n=2/3, 1, 2, and 4, natural inflation, and "hilltop" inflation) using
current data, and provide forecasts for Planck. From current data, we obtain
weak but nontrivial limits on the post-inflationary physics, which is a
significant source of uncertainty in the predictions of inflationary models,
while we find that Planck will dramatically improve these constraints. In
particular, Planck will link the inflationary dynamics with the
post-inflationary growth of the horizon, and thus begin to probe the
"primordial dark ages" between TeV and GUT scale energies.Comment: 16 pages, 9 figures. Updated to match published version (revised and
expanded discussions of reheating uncertainties and slow roll mapping;
references added; results unchanged). Code available at
http://zuserver2.star.ucl.ac.uk/~hiranya/ModeCode
Electron-magnon coupling and nonlinear tunneling transport in magnetic nanoparticles
We present a theory of single-electron tunneling transport through a
ferromagnetic nanoparticle in which particle-hole excitations are coupled to
spin collective modes. The model employed to describe the interaction between
quasiparticles and collective excitations captures the salient features of a
recent microscopic study. Our analysis of nonlinear quantum transport in the
regime of weak coupling to the external electrodes is based on a rate-equation
formalism for the nonequilibrium occupation probability of the nanoparticle
many-body states. For strong electron-boson coupling, we find that the
tunneling conductance as a function of bias voltage is characterized by a large
and dense set of resonances. Their magnetic field dependence in the large-field
regime is linear, with slopes of the same sign. Both features are in agreement
with recent tunneling experiments.Comment: 4 pages, 2 figure
Reconstruction of motional states of neutral atoms via MaxEnt principle
We present a scheme for a reconstruction of states of quantum systems from
incomplete tomographic-like data. The proposed scheme is based on the Jaynes
principle of Maximum Entropy. We apply our algorithm for a reconstruction of
motional quantum states of neutral atoms. As an example we analyze the
experimental data obtained by the group of C. Salomon at the ENS in Paris and
we reconstruct Wigner functions of motional quantum states of Cs atoms trapped
in an optical lattice
Incomplete quantum process tomography and principle of maximal entropy
The main goal of this paper is to extend and apply the principle of maximum
entropy (MaxEnt) to incomplete quantum process estimation tasks. We will define
a so-called process entropy function being the von Neumann entropy of the state
associated with the quantum process via Choi-Jamiolkowski isomorphism. It will
be shown that an arbitrary process estimation experiment can be reformulated in
a unified framework and MaxEnt principle can be consistently exploited. We will
argue that the suggested choice for the process entropy satisfies natural list
of properties and it reduces to the state MaxEnt principle, if applied to
preparator devices.Comment: 8 pages, comments welcome, references adde
Information Theory based on Non-additive Information Content
We generalize the Shannon's information theory in a nonadditive way by
focusing on the source coding theorem. The nonadditive information content we
adopted is consistent with the concept of the form invariance structure of the
nonextensive entropy. Some general properties of the nonadditive information
entropy are studied, in addition, the relation between the nonadditivity
and the codeword length is pointed out.Comment: 9 pages, no figures, RevTex, accepted for publication in Phys. Rev.
E(an error in proof of theorem 1 was corrected, typos corrected
Strong coupling between single photons in semiconductor microcavities
We discuss the observability of strong coupling between single photons in
semiconductor microcavities coupled by a chi(2) nonlinearity. We present two
schemes and analyze the feasibility of their practical implementation in three
systems: photonic crystal defects, micropillars and microdisks, fabricated out
of GaAs. We show that if a weak coherent state is used to enhance the chi(2)
interaction, the strong coupling regime between two modes at different
frequencies occupied by a single photon is within reach of current technology.
The unstimulated strong coupling of a single photon and a photon pair is very
challenging and will require an improvement in mirocavity quality factors of
2-4 orders of magnitude to be observable.Comment: 4 page
James van Allen and his namesake NASA mission
Abstract
In many ways, James A. Van Allen defined and “invented” modern space research. His example showed the way for government-university partners to pursue basic research that also served important national and international goals. He was a tireless advocate for space exploration and for the role of space science in the spectrum of national priorities
Influence of gravitational field on quantum-nondemolition measurement of atomic momentum in the dispersive Jaynes-Cummings model
We present a theoretical scheme based on su(2) algebra to investigate the
influence of homogeneous gravitational field on the quantum nondemolition
measurement of atomic momentum in dispersive Jaynes-Cummings model. In the
dispersive Jaynes-Cummings model, when detuning is large and the atomic motion
is in a propagating light wave, we consider a two-level atom with quantized
cavity-field in the presence of a homogeneous gravitational field. We derive an
effective Hamiltonian describing the dispersive atom-field interaction in the
presence of gravitational field. We can see gravitational influence both on the
momentum filter and momentum distribution. Moreover, gravitational field
decreases both tooth spacing of momentum and the width of teeth of momentum.Comment: 21 pages, 8 figure
On the Bethe Ansatz for the Jaynes-Cummings-Gaudin model
We investigate the quantum Jaynes-Cummings model - a particular case of the
Gaudin model with one of the spins being infinite. Starting from the Bethe
equations we derive Baxter's equation and from it a closed set of equations for
the eigenvalues of the commuting Hamiltonians. A scalar product in the
separated variables representation is found for which the commuting
Hamiltonians are Hermitian. In the semi classical limit the Bethe roots
accumulate on very specific curves in the complex plane. We give the equation
of these curves. They build up a system of cuts modeling the spectral curve as
a two sheeted cover of the complex plane. Finally, we extend some of these
results to the XXX Heisenberg spin chain.Comment: 16 page
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