A simple quantum gate with atom chips

We present a simple scheme for implementing an atomic phase gate using two degrees of freedom for each atom and discuss its realization with cold rubidium atoms on atom chips. We investigate the performance of this collisional phase gate and show that gate operations with high fidelity can be realized in magnetic traps that are currently available on atom chips.Comment: 7 pages, 7 figures. One missing reference added in v2. To appear in European Physical Journal

Stability of a Gaussian pancake vortex in a stratified fluid

International audienceVortices in stably stratified fluids generally have a pancake shape with a small vertical thickness compared with their horizontal size. In order to understand what mechanism determines their minimum thickness, the linear stability of an axisymmetric pancake vortex is investigated as a function of its aspect ratio alpha, the horizontal Froude number F-h, the Reynolds number Re and the Schmidt number Sc. The vertical vorticity profile of the base state is chosen to be Gaussian in both radial and vertical directions. The vortex is unstable when the aspect ratio is below a critical value, which scales with the Froude number: alpha(c) similar to 1.1F(h) for sufficiently large Reynolds numbers. The most unstable perturbation has an azimuthal wavenumber either m = 0, vertical bar m vertical bar = 1 or vertical bar m vertical bar = 2 depending on the control parameters. We show that the threshold corresponds to the appearance of gravitationally unstable regions in the vortex core due to the thermal wind balance. The Richardson criterion for shear instability based on the vertical shear is never satisfied alone. The dominance of the gravitational instability over the shear instability is shown to hold for a general class of pancake vortices with angular velocity of the form (Omega) over tilde (r, z) = Omega(r)f(z) provided that r partial derivative Omega/partial derivative r < 3 Omega everywhere. Finally, the growth rate and azimuthal wavenumber selection of the gravitational instability are accounted well by considering an unstably stratified viscous and diffusive layer in solid body rotation with a parabolic density gradient

CREATION OF A MULTIRESOLUTION AND MULTIACCURACY DTM: PROBLEMS AND SOLUTIONS FOR HELI-DEM CASE STUDY

The work is part of "HELI-DEM" (HELvetia-Italy Digital Elevation Model) project, funded by the European Regional Development Fund within the Italy-Switzerland cooperation program. The aim of the project is the creation of a unique DTM for the alpine and subalpine area between Italy (Piedmont, Lombardy) and Switzerland (Ticino and Grisons Cantons); at present, different DTMs, that are in different reference frames and have been obtained with different technologies, accuracies, and resolutions, have been acquired. The final DTM should be correctly georeferenced and produced validating and integrating the data that are available for the project. DTMs are fundamental in hydrogeological studies, especially in alpine areas where hydrogeological risks may exist. Moreover, when an event, like for example a landslide, happens at the border between countries, a unique and integrated DTM which covers the interest area is useful to analyze the scenario. In this sense, HELI-DEM project is helpful. To perform analyses along the borders between countries, transnational geographic information is needed: a transnational DTM can be obtained by merging regional low resolution DTMs. Moreover high resolution local DTMs should be used where they are available. To be merged, low and high resolution DTMs should be in the same three dimensional reference frame, should not present biases and should be consistent in the overlapping areas. Cross-validation between the different DTMs is therefore needed. Two different problems should be solved: the merging of regional, partly overlapping low and medium resolution DTMs into a unique low/medium resolution DTM and the merging with other local high resolution/high accuracy height data. This paper discusses the preliminary processing of the data for the fusion of low and high resolution DTMs in a study-case area within the Lombardy region: Valtellina valley. In this region the Lombardy regional low resolution DTM is available, with a horizontal resolution of 20 meters; in addition a LiDAR DTM with a horizontal resolution of 1 meter, which covers only the main hydrographic basins, is also available. The two DTMs have been transformed into the same reference frame. The cross-validation of the two datasets has been performed comparing the low resolution DTM with the local high resolution DTM. Then, where significant differences are present, GPS survey have been used as external validation. The results are presented. Moreover, a possible strategy for the future fusion of the data, is shortly summarized at the end of the paper

Trasformazione tra datum e sistemi cartografici in ambito nazionale: implementazione di un software in ambiente GRASS e sue prestazioni

Selected paper presentato a GeoExplora Workshop 2004 - 6° Congresso MondoGIS Il lavoro illustra le caratteristiche e le prestazioni di un comando GRASS sviluppato per gestire le trasformazioni tra i sistemi geodetici (datum), (ed i corrispondenti cartografici) più utilizzati in ambito nazionale, Roma1940 (Gauss-Boaga), ED1950 (UTM-ED1950) e WGS84-ETRF89 (UTMWGS84- ETRF89) per scopi cartografici a scala medio-grande (1:5000)