10 research outputs found
Optical Devices for Cold Atoms and Bose-Einstein Condensates
The manipulation of cold atoms with optical fields is a very promising
technique for a variety of applications ranging from laser cooling and trapping
to coherent atom transport and matter wave interferometry. Optical fields have
also been proposed as interesting tools for quantum information processing with
cold atoms. In this paper, we present a theoretical study of the dynamics of a
cold 87Rb atomic cloud falling in the gravity field in the presence of two
crossing dipole guides. The cloud is either deflected or split between the two
branches of this guide. We explore the possibilities of optimization of this
device and present preliminary results obtained in the case of zero-temperature
dilute Bose-Einstein condensates.Comment: Proceedings of the International Spectroscopy Conference ISC-2007,
Sousse, Tunisi
Theoretical study of a cold atom beam splitter
A theoretical model is presented for the study of the dynamics of a cold
atomic cloud falling in the gravity field in the presence of two crossing
dipole guides. The cloud is split between the two branches of this laser guide,
and we compare experimental measurements of the splitting efficiency with
semiclassical simulations. We then explore the possibilities of optimization of
this beam splitter. Our numerical study also gives access to detailed
information, such as the atom temperature after the splitting
Bose-Einstein condensation with a finite number of particles in a power-law trap
International audienceBose-Einstein condensation (BEC) of an ideal gas is investigated, beyond the thermodynamic limit, for a finite number of particles trapped in a generic three-dimensional power-law potential. We derive an analytical expression for the condensation temperature in terms of a power series in , where denotes the zero-point energy of the trapping potential. This expression, which applies in cartesian, cylindrical and spherical power-law traps, is given analytically at infinite order. It is also given numerically for specific potential shapes as an expansion in powers of up to the second order. We show that, for a harmonic trap, the well known first order shift of the critical temperature is inaccurate when , the next order (proportional to ) being significant. We also show that finite size effects on the condensation temperature cancel out in a cubic trapping potential, \textit{e.g.} V(\mathbi{r}) \propto r^3. Finally, we show that in a generic power-law potential of higher order, \textit{e.g.} V(\mathbi{r}) \propto r^\alpha with , the shift of the critical temperature becomes positive. This effect provides a large increase of for relatively small atom numbers. For instance, an increase of about +40\% is expected with atoms in a V(\mathbi{r}) \propto r^{12} trapping potential
Dynamique d'atomes froids dans des potentiels optiques façonnés
Dans ce mémoire, nous présentons tout d'abord, une étude théorique de génération de condensats de Bose-Einstein (BEC) façonnés. Le façonnage se fait en utilisant des faisceaux lasers en modes Laguerre-Gauss (LG) décalés vers le bleu. Ces modes possèdent un nœud au centre et piègent les atomes dans une géométrie cylindrique autour de l'axe de propagation. On analyse l'effet de variation de l'indice azimutal du champ électrique du laser qui définira le potentiel de piégeage. Des géométries 1D (cigare), 2D (disque) et 3D (sphère) seront explorées. On présente ensuite l'étude de la dynamique de croissance du condensat en se basant sur la théorie cinétique quantique. Notre étude montre que pour un volume de piège fixe, la température de condensation croit et la durée de croissance décroît significativement en fonction de l'indice azimutal du faisceau LG. Dans une seconde partie, on étudie une autre dynamique de condensat en chute dans le champ de gravité et en présence de deux guides dipolaires croisés fournis par des faisceaux gaussiens. On étudie la déflexion du condensat en résolvant l'équation de Gross-Pitaevskii dépendante de temps. On discute les possibilités d'optimisation de ce dispositif de déflexion et présente des résultats obtenus dans le cas d'un condensat à basse température.ln this thesis, at first we present a realistic theoretical model for generating shaped Bose-Einstein condensates (BECs) of a dilute atomic system, employing blue detuned Laguerre-Gauss (LG) laser beams. Such laser beams have modes which show anode in the center, and trap the atoms in a cylindrical geometry around the axis of propagation of the beam. We study the effect of changing the azimuthal index of the optical potential generated by these beams. One-dimensional (cigar-shape), two-dimensional (disk-shape) and three-dimensional (cylindrical-shape) condensate geometries are explored. We then present an analysis of the BEC growth dynamics, using the quantum kinetic theory. Our study shows that, for a fixed volume of the trap, the temperature of condensation increases substantially and the growth duration decreases significantly with the azimuthal index of the LG beam. Then we present another aspect of the study of the dynamics of a BEC falling in the gravity field in the presence of two crossing dipoles guides. We study the deflexion of the BEC by solving the time-dependent Gross-Pitaevskii equation. We explore the possibilities of optimization of this device and present results obtained in the case of low temperature dilute Bose-Einstein condensates.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF
Étude théorique de la manipulation laser d'atomes froids
ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceTunisiaFRT
Isotopic Effect in LiD and BeD Formation through Radiative Association
International audienc
Isotopic Effect in LiD and BeD Formation through Radiative Association
International audienc