184 research outputs found
Oscillations of a Bose-Einstein condensate rotating in a harmonic plus quartic trap
We study the normal modes of a two-dimensional rotating Bose-Einstein
condensate confined in a quadratic plus quartic trap. Hydrodynamic theory and
sum rules are used to derive analytical predictions for the collective
frequencies in the limit of high angular velocities, , where the vortex
lattice produced by the rotation exhibits an annular structure. We predict a
class of excitations with frequency in the rotating frame,
irrespective of the mode multipolarity , as well as a class of low energy
modes with frequency proportional to . The predictions are in good
agreement with results of numerical simulations based on the 2D
Gross-Pitaevskii equation. The same analysis is also carried out at even higher
angular velocities, where the system enters the giant vortex regime.Comment: 4 pages, 2 figure
Fermi Gases in Slowly Rotating Traps: Superfluid vs Collisional Hydrodynamics
The dynamic behavior of a Fermi gas confined in a deformed trap rotating at
low angular velocity is investigated in the framework of hydrodynamic theory.
The differences exhibited by a normal gas in the collisional regime and a
superfluid are discussed. Special emphasis is given to the collective
oscillations excited when the deformation of the rotating trap is suddenly
removed or when the rotation is suddenly stopped. The presence of vorticity in
the normal phase is shown to give rise to precession and beating phenomena
which are absent in the superfluid phase.Comment: 4 pages, 2 figure
Vortex signatures in annular Bose-Einstein condensates
We consider a Bose-Einstein condensate confined in a ``Mexican hat''
potential, with a quartic minus quadratic radial dependence. We find conditions
under which the ground state is annular in shape, with a hole in the center of
the condensate. Rotation leads to the appearance of stable multiply-quantized
vortices, giving rise to a superfluid flow around the ring. The collective
modes of the system are explored both numerically and analytically using the
Gross-Pitaevskii and hydrodynamic equations. Potential experimental schemes to
detect vorticity are proposed and evaluated, which include measuring the
splitting of collective mode frequencies, observing expansion following release
from the trap, and probing the momentum distribution of the condensate.Comment: 11 pages, 7 figure
Diffused vorticity approach to the oscillations of a rotating Bose-Einstein condensate confined in a harmonic plus quartic trap
The collective modes of a rotating Bose-Einstein condensate confined in an
attractive quadratic plus quartic trap are investigated. Assuming the presence
of a large number of vortices we apply the diffused vorticity approach to the
system. We then use the sum rule technique for the calculation of collective
frequencies, comparing the results with the numerical solution of the
linearized hydrodynamic equations. Numerical solutions also show the existence
of low-frequency multipole modes which are interpreted as vortex oscillations.Comment: 10 pages, 4 figure
Tkachenko oscillations and the compressibility of a rotating Bose gas
The elastic oscillations of the vortex lattice of a cold Bose gas (Tkachenko
modes) are shown to play a crucial role in the saturation of the
compressibility sum rule, as a consequence of the hybridization with the
longitudinal degrees of freedom. The presence of the vortex lattice is
responsible for a behavior of the static structure factor at small
wavevectors , which implies the absence of long range order in 2D
configurations at zero temperature. Sum rules are used to calculate the
Tkachenko frequency in the presence of harmonic trapping. Results are derived
in the Thomas-Fermi regime and compared with experiments as well as with
previous theoretical estimates.Comment: 4 pages, 2 figure
Emotion-based analysis of programming languages on Stack Overflow
When developing a software engineering project, selecting the most appropriate programming language is a crucial step. Most often, feeling at ease with the possible options becomes almost as relevant as the technical features of the language. Therefore, it appears to be worth analyzing the role that the emotional component plays in this process. In this article, we analyze the trend of the emotions expressed by developers in 2018 on the Stack Overflow platform in posts concerning 26 programming languages. To do so, we propose a learning model trained by distant supervision and the comparison of two different classifier architectures
A Textured Silicon Calorimetric Light Detector
We apply the standard photovoltaic technique of texturing to reduce the
reflectivity of silicon cryogenic calorimetric light detectors. In the case of
photons with random incidence angles, absorption is compatible with the
increase in surface area. For the geometrically thin detectors studied, energy
resolution from athermal phonons, dominated by position dependence, is
proportional to the surface-to-volume ratio. With the CaWO4 scintillating
crystal used as light source, the time constants of the calorimeter should be
adapted to the relatively slow light-emission times.Comment: Submitted to Journal of Applied Physic
Generalized Coherent States as Preferred States of Open Quantum Systems
We investigate the connection between quasi-classical (pointer) states and
generalized coherent states (GCSs) within an algebraic approach to Markovian
quantum systems (including bosons, spins, and fermions). We establish
conditions for the GCS set to become most robust by relating the rate of purity
loss to an invariant measure of uncertainty derived from quantum Fisher
information. We find that, for damped bosonic modes, the stability of canonical
coherent states is confirmed in a variety of scenarios, while for systems
described by (compact) Lie algebras stringent symmetry constraints must be
obeyed for the GCS set to be preferred. The relationship between GCSs,
minimum-uncertainty states, and decoherence-free subspaces is also elucidated.Comment: 5 pages, no figures; Significantly improved presentation, new
derivation of invariant uncertainty measure via quantum Fisher information
added
The fidelity approach to the Hubbard model
We use the fidelity approach to quantum critical points to study the zero
temperature phase diagram of the one-dimensional Hubbard model. Using a variety
of analytical and numerical techniques, we analyze the fidelity metric in
various regions of the phase diagram, with particular care to the critical
points. Specifically we show that close to the Mott transition, taking place at
on-site repulsion U=0 and electron density n=1, the fidelity metric satisfies
an hyper-scaling form which we calculate. This implies that in general, as one
approaches the critical point U=0, n=1, the fidelity metric tends to a limit
which depends on the path of approach. At half filling, the fidelity metric is
expected to diverge as U^{-4} when U is sent to zero.Comment: 8 pages, 4 figures, added results on the hyper-scaling form of the
fidelity metri
CdWO4 scintillating bolometer for Double Beta Decay: Light and Heat anticorrelation, light yield and quenching factors
We report the performances of a 0.51 kg CdWO4 scintillating bolometer to be
used for future Double Beta Decay Experiments. The simultaneous read-out of the
heat and the scintillation light allows to discriminate between different
interacting particles aiming at the disentanglement and the reduction of
background contribution, key issue for next generation experiments. We will
describe the observed anticorrelation between the heat and the light signal and
we will show how this feature can be used in order to increase the energy
resolution of the bolometer over the entire energy spectrum, improving up to a
factor 2.6 on the 2615 keV line of 208Tl. The detector was tested in a 433 h
background measurement that permitted to estimate extremely low internal trace
contaminations of 232Th and 238U. The light yield of gamma/beta, alpha and
neutrons is presented. Furthermore we developed a method in order to correctly
evaluate the absolute thermal quenching factor of alpha particles in
scintillating bolometers.Comment: 8 pages 7 figure
- …