70 research outputs found
Exact numerical methods for a many-body Wannier Stark system
We present exact methods for the numerical integration of the Wannier-Stark
system in a many-body scenario including two Bloch bands. Our ab initio
approaches allow for the treatment of a few-body problem with bosonic
statistics and strong interparticle interaction. The numerical implementation
is based on the Lanczos algorithm for the diagonalization of large, but sparse
symmetric Floquet matrices. We analyze the scheme efficiency in terms of the
computational time, which is shown to scale polynomially with the size of the
system. The numerically computed eigensystem is applied to the analysis of the
Floquet Hamiltonian describing our problem. We show that this allows, for
instance, for the efficient detection and characterization of avoided crossings
and their statistical analysis. We finally compare the efficiency of our
Lanczos diagonalization for computing the temporal evolution of our many-body
system with an explicit fourth order Runge-Kutta integration. Both
implementations heavily exploit efficient matrix-vector multiplication schemes.
Our results should permit an extrapolation of the applicability of exact
methods to increasing sizes of generic many-body quantum problems with bosonic
statistics
The prison system of Colombia and practices to transform process resocialization
Descripción actual del sistema carcelario de Colombia y practicas para mejorar el proceso de resocialización en las personas privadas de la libertad.Actual description of Colombia's prison system and practices to improve the process of rehabilitation in persons deprived of freedo
Ericson fluctuations in an open, deterministic quantum system: theory meets experiment
We provide numerically exact photoexcitation cross sections of rubidium
Rydberg states in crossed, static electric and magnetic fields, in quantitative
agreement with recent experimental results. Their spectral backbone underpins a
clear transition towards the Ericson regime.Comment: 4 pages, 3 figures, 1 tabl
Cold atom-ion systems in radiofrequency multipole traps: event-drive molecular dynamics and stochastic simulations
We have studied the general aspects of the dynamics of an ion trapped in an
ideal multipolar radiofrequency trap while interacting with a dense cold atomic
gas. In particular, we have explored the dynamical stability, the energy
relaxation and the characteristic harmonic motion exhibited by a trapped
Yb ion in different multipolar potentials and immersed in various cold
atomic samples (Li, Na, Rb, Yb). For this purpose, we used two different
molecular dynamics simulations; one based on a time-event drive algorithm and
the other based on the stochastic Langevin equation. Relevant values for
experimental realizations, such as the associated ion's lifetimes and
observable distributions, are presented along with some analytical expressions
which relate the ion's dynamical properties with the trap parameters.Comment: 12 pages, 11 figure
“Método perfecto” Alternativa tecnológica para el cálculo y construcción del diapasón en instrumentos de cuerda pulsada
Este proyecto trata de una alternativa que por medio de la utilización de las herramientas informáticas actúales busca facilitar el trabajo del lutier y volverlo mas exacto en el momento de calcular y construir el diapasón en instrumentos de cuerda pulsada. En esta propuesta se utiliza software como Excel para realizar el cálculo exacto de las medidas de cada espacio entre traste y traste y CorelDRAW para diseñar una plantilla la cual servirá para modificar únicamente su largo y servirá para obtener la medida que sea necesaria de manera rápida y precisa
Explicit schemes for time propagating many-body wavefunctions
Accurate theoretical data on many time-dependent processes in atomic and
molecular physics and in chemistry require the direct numerical solution of the
time-dependent Schr\"odinger equation, thereby motivating the development of
very efficient time propagators. These usually involve the solution of very
large systems of first order differential equations that are characterized by a
high degree of stiffness. We analyze and compare the performance of the
explicit one-step algorithms of Fatunla and Arnoldi. Both algorithms have
exactly the same stability function, therefore sharing the same stability
properties that turn out to be optimum. Their respective accuracy however
differs significantly and depends on the physical situation involved. In order
to test this accuracy, we use a predictor-corrector scheme in which the
predictor is either Fatunla's or Arnoldi's algorithm and the corrector, a fully
implicit four-stage Radau IIA method of order 7. We consider two physical
processes. The first one is the ionization of an atomic system by a short and
intense electromagnetic pulse; the atomic systems include a one-dimensional
Gaussian model potential as well as atomic hydrogen and helium, both in full
dimensionality. The second process is the decoherence of two-electron quantum
states when a time independent perturbation is applied to a planar two-electron
quantum dot where both electrons are confined in an anharmonic potential. Even
though the Hamiltonian of this system is time independent the corresponding
differential equation shows a striking stiffness. For the one-dimensional
Gaussian potential we discuss in detail the possibility of monitoring the time
step for both explicit algorithms. In the other physical situations that are
much more demanding in term of computations, we show that the accuracy of both
algorithms depends strongly on the degree of stiffness of the problem.Comment: 24 pages, 14 Figure
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