34,973 research outputs found
Loading of a Bose-Einstein condensate in the boson-accumulation regime
We study the optical loading of a trapped Bose-Einstein condensate by
spontaneous emission of atoms in excited electronic state in the
Boson-Accumulation Regime. We generalize the previous simplified analysis of
ref. [Phys. Rev. A 53, 2466 (1996)], to a 3D case in which more than one trap
level of the excited state trap is considered. By solving the corresponding
quantum many-body master equation, we demonstrate that also for this general
situation the photon reabsorption can help to increase the condensate fraction.
Such effect could be employed to realize a continuous atom laser, and to
overcome condensate losses.Comment: 7 pages, 5 eps figures, uses epl.st
Manipulation of the dynamics of many-body systems via quantum control methods
We investigate how dynamical decoupling methods may be used to manipulate the
time evolution of quantum many-body systems. These methods consist of sequences
of external control operations designed to induce a desired dynamics. The
systems considered for the analysis are one-dimensional spin-1/2 models, which,
according to the parameters of the Hamiltonian, may be in the integrable or
non-integrable limits, and in the gapped or gapless phases. We show that an
appropriate control sequence may lead a chaotic chain to evolve as an
integrable chain and a system in the gapless phase to behave as a system in the
gapped phase. A key ingredient for the control schemes developed here is the
possibility to use, in the same sequence, different time intervals between
control operations.Comment: 10 pages, 3 figure
2DPHOT: A Multi-purpose Environment for the Two-dimensional Analysis of Wide-field Images
We describe 2DPHOT, a general purpose analysis environment for source
detection and analysis in deep wide-field images. 2DPHOT is an automated tool
to obtain both integrated and surface photometry of galaxies in an image, to
perform reliable star-galaxy separation with accurate estimates of
contamination at faint flux levels, and to estimate completeness of the image
catalog. We describe the analysis strategy on which 2DPHOT is based, and
provide a detailed description of the different algorithms implemented in the
package. This new environment is intended as a dedicated tool to process the
wealth of data from wide-field imaging surveys. To this end, the package is
complemented by 2DGUI, an environment that allows multiple processing of data
using a range of computing architectures.Comment: Accepted to PAS
Structure of penetrable-rod fluids: Exact properties and comparison between Monte Carlo simulations and two analytic theories
Bounded potentials are good models to represent the effective two-body
interaction in some colloidal systems, such as dilute solutions of polymer
chains in good solvents. The simplest bounded potential is that of penetrable
spheres, which takes a positive finite value if the two spheres are overlapped,
being 0 otherwise. Even in the one-dimensional case, the penetrable-rod model
is far from trivial, since interactions are not restricted to nearest neighbors
and so its exact solution is not known. In this paper we first derive the exact
correlation functions of penetrable-rod fluids to second order in density at
any temperature, as well as in the high-temperature and zero-temperature limits
at any density. Next, two simple analytic theories are constructed: a
high-temperature approximation based on the exact asymptotic behavior in the
limit and a low-temperature approximation inspired by the exact
result in the opposite limit . Finally, we perform Monte Carlo
simulations for a wide range of temperatures and densities to assess the
validity of both theories. It is found that they complement each other quite
well, exhibiting a good agreement with the simulation data within their
respective domains of applicability and becoming practically equivalent on the
borderline of those domains. A perspective on the extension of both approaches
to the more realistic three-dimensional case is provided.Comment: 19 pages, 11 figures, 4 tables: v2: minor changes; published final
versio
Diffraction and an infrared finite gluon propagator
We discuss some phenomenological applications of an infrared finite gluon
propagator characterized by a dynamically generated gluon mass. In particular
we compute the effect of the dynamical gluon mass on and
diffractive scattering. We also show how the data on photoproduction
and hadronic reactions can be derived from the and
forward scattering amplitudes by assuming vector meson dominance and
the additive quark model.Comment: 4 pages, 7 figures, added references and figures, changed structure.
Contribution to Proceedings of XVIIIth Reuniao de Trabalho sobre Interacoes
Hadronicas, Sao Paulo, Brazil, 22-24 May, 200
Evolution of squeezed states under the Fock-Darwin Hamiltonian
We develop a complete analytical description of the time evolution of
squeezed states of a charged particle under the Fock-Darwin Hamiltonian and a
time-dependent electric field. This result generalises a relation obtained by
Infeld and Pleba\'nski for states of the one-dimensional harmonic oscillator.
We relate the evolution of a state-vector subjected to squeezing to that of
state which is not subjected to squeezing and for which the time-evolution
under the simple harmonic oscillator dynamics is known (e.g. an eigenstate of
the Hamiltonian). A corresponding relation is also established for the Wigner
functions of the states, in view of their utility in the analysis of cold-ion
experiments. In an appendix, we compute the response functions of the FD
Hamiltonian to an external electric field, using the same techniques as in the
main text
Observational constraints on modified gravity models and the Poincar\'e dodecahedral topology
We study the constraints that spatial topology may place on the parameters of
models that account for the accelerated expansion of the universe via infrared
modifications to general relativity, namely the Dvali-Gabadadze-Porrati
braneworld model as well as the Dvali-Turner and Cardassian models. By
considering the Poincar\'e dodecahedral space as the circles-in-the-sky
observable spatial topology, we examine the constraints that can be placed on
the parameters of each model using type Ia supernovae data together with the
baryon acoustic peak in the large scale correlation function of the Sloan
Digital Sky Survey of luminous red galaxies and the Cosmic Microwave Background
Radiation shift parameter data. We show that knowledge of spatial topology does
provide relevant constraints, particularly on the curvature parameter, for all
models.Comment: Revtex4, 10 pages, 1 table, 12 figures; version to match the one to
be published in Physical Review
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