4,841 research outputs found
Using boundary methods to compute the Casimir energy
We discuss new approaches to compute numerically the Casimir interaction
energy for waveguides of arbitrary section, based on the boundary methods
traditionally used to compute eigenvalues of the 2D Helmholtz equation. These
methods are combined with the Cauchy's theorem in order to perform the sum over
modes. As an illustration, we describe a point-matching technique to compute
the vacuum energy for waveguides containing media with different
permittivities. We present explicit numerical evaluations for perfect
conducting surfaces in the case of concentric corrugated cylinders and a
circular cylinder inside an elliptic one.Comment: To be published in the Proceedings of QFEXT09, Norman, OK
Dynamical Casimir effect in superconducting circuits: a numerical approach
We present a numerical analysis of the particle creation for a quantum field
in the presence of time dependent boundary conditions. Having in mind recent
experiments involving superconducting circuits, we consider their description
in terms of a scalar field in a one dimensional cavity satisfying generalized
boundary conditions that involve a time-dependent linear combination of the
field and its spatial and time derivatives. We evaluate numerically the
Bogoliubov transformation between {\it in} and {\it out}-states and find that
the rate of particle production strongly depends on whether the spectrum of the
unperturbed cavity is equidistant or not, and also on the amplitude of the
temporal oscillations of the boundary conditions. We provide analytic
justifications for the different regimes found numerically.Comment: 20 pages. 11 figure
Geometric phases under the presence of a composite environment
We compute the geometric phase for a spin-1/2 particle under the presence of
a composite environment, composed of an external bath (modeled by an infinite
set of harmonic oscillators) and another spin-1/2 particle. We consider both
cases: an initial entanglement between the spin-1/2 particles and an initial
product state in order to see if the initial entanglement has an enhancement
effect on the geometric phase of one of the spins. We follow the nonunitary
evolution of the reduced density matrix and evaluate the geometric phase for a
single two-level system. We also show that the initial entanglement enhances
the sturdiness of the geometric phase under the presence of an external
composite environment.Comment: 10 pages, 12 figures. Version to appear in Phys. Rev.
Dephasing in matter-wave interferometry
We review different attempts to show the decoherence process in
double-slit-like experiments both for charged particles (electrons) and neutral
particles with permanent dipole moments. Interference is studied when electrons
or atomic systems are coupled to classical or quantum electromagnetic fields.
The interaction between the particles and time-dependent fields induces a
time-varying Aharonov phase. Averaging over the phase generates a suppression
of fringe visibility in the interference pattern. We show that, for suitable
experimental conditions, the loss of contrast for dipoles can be almost as
large as the corresponding one for coherent electrons and therefore, be
observed. We analyze different trajectories in order to show the dependence of
the decoherence factor with the velocity of the particles.Comment: 9 pages, 1 eps-figure. To appear in J. Phys. A: Math. Ge
Decoherence in a Two Slit Diffraction Experiment with Massive Particles
Matter-wave interferometry has been largely studied in the last few years.
Usually, the main problem in the analysis of the diffraction experiments is to
establish the causes for the loss of coherence observed in the interference
pattern. In this work, we use different type of environmental couplings to
model a two slit diffraction experiment with massive particles. For each model,
we study the effects of decoherence on the interference pattern and define a
visibility function that measures the loss of contrast of the interference
fringes on a distant screen. Finally, we apply our results to the experimental
reported data on massive particles .Comment: 6 pages, 3 figure
Transition to Chaotic Phase Synchronization through Random Phase Jumps
Phase synchronization is shown to occur between opposite cells of a ring
consisting of chaotic Lorenz oscillators coupled unidirectionally through
driving. As the coupling strength is diminished, full phase synchronization
cannot be achieved due to random generation of phase jumps. The brownian
dynamics underlying this process is studied in terms of a stochastic diffusion
model of a particle in a one-dimensional medium.Comment: Accepted for publication in IJBC, 10 pages, 5 jpg figure
Analysis of backgrounds for the ANAIS-112 dark matter experiment
The ANAIS (Annual modulation with NaI(Tl) Scintillators) experiment aims at
the confirmation or refutation of theDAMA/LIBRA positive annual modulation
signal in the low energy detection rate, using the same target and technique,
at the Canfranc Underground Laboratory (LSC) in Spain. ANAIS-112, consisting of
nine 12.5 kg NaI(Tl) modules produced by Alpha Spectra Inc. in a 3x3matrix
configuration, is taking data smoothly in "dark matter search" mode since
August, 2017, after a commissioning phase and operation of the first detectors
during the last years in various setups. A large effort has been carried out
withinANAIS to characterize the background of sodium iodide detectors, before
unblinding the data and performing the first annual modulation analysis. Here,
the background models developed for all the nine ANAIS-112 detectors are
presented. Measured spectra from threshold to high energy in different
conditions are well described by the models based on quantified activities
independently estimated following several approaches. In the region from 1 to 6
keVee the measured, efficiency corrected background level is 3.58+-0.02 keV-1
kg-1 day-1; NaI crystal bulk contamination is the dominant background source
being 210Pb, 40K, 22Na and 3H contributions the most relevant ones. This
background level, added to the achieved 1 keVee analysis threshold (thanks to
the outstanding light collection and robust filtering procedures developed),
allow ANAIS-112 to be sensitive to the modulation amplitude measured by
DAMA/LIBRA, and able to explore at three sigma level in 5 years the WIMP
parameter region singled out by this experiment.Comment: Final version for publicatio
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