Tkachenko polarons in vortex lattices

We analyze the properties of impurities immersed in a vortex lattice formed by ultracold bosons in the mean field quantum Hall regime. In addition to the effects of a periodic lattice potential, the impurity is dressed by collective modes with parabolic dispersion (Tkachenko modes). We derive the effective polaron model, which contains a marginal impurity-phonon interaction. The polaron spectral function exhibits a Lorentzian broadening for arbitrarily small wave vectors even at zero temperature, in contrast with the result for optical or acoustic phonons. The anomalous damping of Tkachenko polarons could be detected experimentally using momentum-resolved spectroscopy.Comment: 10 pages, 2 figure

Capture Velocity for a Magneto-Optical Trap in a Broad Range of Light Intensity

In a recent paper, we have used the dark-spot Zeeman tuned slowing technique [Phys. Rev. A 62, 013404-1, (2000)] to measure the capture velocity as a function of laser intensity for a sodium magneto optical trap. Due to technical limitation we explored only the low light intensity regime, from 0 to 27 mW/cm^2. Now we complement that work measuring the capture velocity in a broader range of light intensities (from 0 to 400 mW/cm^2). New features, observed in this range, are important to understant the escape velocity behavior, which has been intensively used in the interpretation of cold collisions. In particular, we show in this brief report that the capture velocity has a maximum as function of the trap laser intensity, which would imply a minimum in the trap loss rates.Comment: 2 pages, 2 figure

Student Exchange in Japan: Why and How to Provide Engineering Students with an International Experience

In the last years, to improve the performance of prediction of radioactive contamination, an increasing number of studies have explored and exploited the potentials of geostatistical methods. However, traditional methods like kriging and cokriging are optimal only in the case in which the data may be assumed Gaussian and do not properly cope with data measurements that are discrete, nonnegative or show some degree of skewness, as in many environmental applications concerned with radioactivity measurements. To deal with geostatistical skewed data, we consider a model-based approach in which measurements are modeled with the help of a latent Gaussian structure and some recent classes of skewed distributions extending the normal one. For our model we investigate the implied spatial autocorrelation structure and the marginal distributions of the observable variables. In particular we show that all finite-dimensional marginal distributions of the observable variables belong to the family of the unified skew-normal distribution. Estimation of some of the unknown parameters of the model can be carried out by employing a Monte Carlo expectation maximization procedure, whereas predictions of both latent and observed (at unsampled sites) variables, can be supplied by Markov chain Monte Carlo algorithms

Simple analysis of off-axis solenoid fields using the scalar magnetostatic potential: application to a Zeeman-slower for cold atoms

In a region free of currents, magnetostatics can be described by the Laplace equation of a scalar magnetic potential, and one can apply the same methods commonly used in electrostatics. Here we show how to calculate the general vector field inside a real (finite) solenoid, using only the magnitude of the field along the symmetry axis. Our method does not require integration or knowledge of the current distribution, and is presented through practical examples, including a non-uniform finite solenoid used to produce cold atomic beams via laser cooling. These examples allow educators to discuss the non-trivial calculation of fields off-axis using concepts familiar to most students, while offering the opportunity to introduce important advancements of current modern research.Comment: 6 pages. Accepted in the American Journal of Physic

Emergence of turbulence in an oscillating Bose-Einstein condensate

We report on the experimental observation of vortices tangle in an atomic BEC of Rb-87 atoms when an external oscillatory perturbation is introduced in the trap. The vortices tangle configuration is a signature of the presence of a turbulent regime in the cloud. We also show that this turbulent cloud has suppression of the aspect ratio inversion typically observed in quantum degenerate bosonic gases during free expansion. Instead, the cloud expands keeping the ratio between their axis constant. Turbulence in atomic superfluids may constitute an alternative system to investigate decay mechanisms as well as to test fundamental theoretical aspects in this field.Comment: accepted for Phys. Rev. Let