2,367 research outputs found
Atom laser dynamics in a tight-waveguide
We study the transient dynamics that arise during the formation of an atom
laser beam in a tight waveguide. During the time evolution the density profile
develops a series of wiggles which are related to the diffraction in time
phenomenon. The apodization of matter waves, which relies on the use of smooth
aperture functions, allows to suppress such oscillations in a time interval,
after which there is a revival of the diffraction in time. The revival time
scale is directly related to the inverse of the harmonic trap frequency for the
atom reservoir.Comment: 6 pages, 5 figures, to be published in the Proceedings of the 395th
WE-Heraeus Seminar on "Time Dependent Phenomena in Quantum Mechanics ",
organized by T. Kramer and M. Kleber (Blaubeuren, Germany, September 2007
Is the cosmological dark sector better modeled by a generalized Chaplygin gas or by a scalar field?
Both scalar fields and (generalized) Chaplygin gases have been widely used
separately to characterize the dark sector of the Universe. Here we investigate
the cosmological background dynamics for a mixture of both these components and
quantify the fractional abundances that are admitted by observational data from
supernovae of type Ia and from the evolution of the Hubble rate. Moreover, we
study how the growth rate of (baryonic) matter perturbations is affected by the
dark-sector perturbations.Comment: 20 pages, 9 figures, substantially revised, section on matter
perturbations added, accepted for publication in EPJ
Cosmology with Ricci-type dark energy
We consider the dynamics of a cosmological substratum of pressureless matter
and holographic dark energy with a cutoff length proportional to the Ricci
scale. Stability requirements for the matter perturbations are shown to single
out a model with a fixed relation between the present matter fraction
and the present value of the equation-of-state
parameter of the dark energy. This model has the same number of free parameters
as the CDM model but it has no CDM limit. We discuss the
consistency between background observations and the mentioned
stability-guaranteeing parameter combination.Comment: 6 pages, 3 figures, submitted to the Proceedings of the CosmoSurII
conference, Valpara\'iso, Chile, 27 - 31 May 201
Diffraction in time of a confined particle and its Bohmian paths
Diffraction in time of a particle confined in a box which its walls are
removed suddenly at is studied. The solution of the time-dependent
Schr\"{o}dinger equation is discussed analytically and numerically for various
initial wavefunctions. In each case Bohmian trajectories of the particles are
computed and also the mean arrival time at a given location is studied as a
function of the initial state.Comment: 8 pages, 6 figure
Curvature in causal BD-type inflationary cosmology
We study a closed model of the universe filled with viscous fluid and
quintessence matter components in a Brans-Dicke type cosmological model. The
dynamical equations imply that the universe may look like an accelerated flat
Friedmann-Robertson-Walker universe at low redshift. We consider here
dissipative processes which follow a causal thermodynamics. The theory is
applied to viscous fluid inflation, where accepted values for the total entropy
in the observable universe is obtained.Comment: 11 pages, revtex 4. For a festschrift honoring Alberto Garcia. To be
publishen in Gen. Rel. Gra
Quantum Simulation of Dissipative Processes without Reservoir Engineering
We present a quantum algorithm to simulate general finite dimensional
Lindblad master equations without the requirement of engineering the
system-environment interactions. The proposed method is able to simulate both
Markovian and non-Markovian quantum dynamics. It consists in the quantum
computation of the dissipative corrections to the unitary evolution of the
system of interest, via the reconstruction of the response functions associated
with the Lindblad operators. Our approach is equally applicable to dynamics
generated by effectively non-Hermitian Hamiltonians. We confirm the quality of
our method providing specific error bounds that quantify itss accuracy.Comment: 7 pages + Supplemental Material (6 pages
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