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 $N$ of particles trapped in a generic three-dimensional power-law potential. We derive an analytical expression for the condensation temperature $T_c$ in terms of a power series in $x_0=\varepsilon_0/k_BT_c$, where $\varepsilon_0$ 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 $x_0$ up to the second order. We show that, for a harmonic trap, the well known first order shift of the critical temperature $\Delta T_c/T_c \propto N^{-1/3}$ is inaccurate when $N \leqslant 10^{5}$, the next order (proportional to $N^{-1/2}$) 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 $\alpha > 3$, the shift of the critical temperature becomes positive. This effect provides a large increase of $T_c$ for relatively small atom numbers. For instance, an increase of about +40\% is expected with $10^4$ 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

Isotopic Effect in LiD and BeD Formation through Radiative Association

International audienc