Realization of tunnel barriers for matter waves using spatial gaps

We experimentally demonstrate the trapping of a propagating Bose-Einstein Condensate in a Bragg cavity produced by an attractive optical lattice with a smooth envelope. As a consequence of the envelope, the band gaps become position-dependent and act as mirrors of finite and velocity-dependent reflectivity. We directly observe both the oscillations of the wave packet bouncing in the cavity provided by these spatial gaps and the tunneling out for narrow classes of velocity. Synchronization of different classes of velocity can be achieved by proper shaping of the envelope. This technique can generate single or multiple tunnel barriers for matter waves with a tunable transmission probability, equivalent to a standard barrier of submicron size

Guided atom laser: transverse mode quality and longitudinal momentum distribution

We analyze the outcoupling of a matter wave into a guide by a time-dependent spilling of the atoms from an initially trapped Bose-Einstein condensate. This process yields intrinsically a breakdown of the adiabatic condition that triggers the outcoupling of the wave function. Our analysis of the time-dependent engineering and manipulation of condensates in momentum space in this context enables to work out the limits due to interactions in the mode quality of a guided atom laser. This study is consistent with recent experimental observations of low transverse excitations of guided atom lasers and suggests (i) an optimal strategy to realize such quasi-monomode guided atom lasers with, in addition, the lowest possible longitudinal velocity dispersion, or alternatively (ii) a strategy for engineering the atomic flux of the atom laser.Comment: Phys. Rev. A 84, 043618 (2011

Matter wave scattering on complex potentials

La première partie de cette thèse présente le développement d'un nouveau type de ralentisseur à effet Zeeman à aimants permanents qui possède certains avantages par rapport à la réalisation conventionnelle. Les performances des ces dispositifs sont discutées pour deux configurations d'aimants : \emph{dipole} et \emph{Halbach}. La deuxième partie porte sur des expériences de diffusion d'onde de matière guidées sur des potentiels complexes. Après avoir décrit le système expérimental qui permet la production de condensats de Bose-Einstein dans un piège dipolaire croisé, trois expériences sont successivement présentées. La première décrit la diffusion d'une onde de matière sur un réseau optique de taille finie qui réalise un miroir de Bragg. Les processus à l'œuvre sont discutés et la transmission à travers le miroir est caractérisée. Nous démontrons ensuite le piégeage d'un condensat à l'intérieur d'une cavité de Bragg fournie par l'envelope du reseau optique. Nous observons des oscillations dans la cavité ainsi que la sortie de la cavité par effet tunnel de certaines classes de vitesse. Cette technique permet de caractériser des barrières tunnel dans l'espace des position équivalentes à une barrière repulsive submicronique. Finalement, nous présentons la diffusion d'une onde de matière sur un réseau modulé en amplitude et étudions la transmission à travers cette structure en fonction de la fréquence de la modulation. La dynamique complexe en jeu est décrite grâce au formalisme de Floquet-Bloch. Cette technique permet de réaliser un nouveau type de filtre accordable en vitesse. Ce filtre à l'avantage de ne pas dépendre d'une structure interne spécifiqueThe first part of this thesis concerns the development of a novel type of Zeeman slower (ZS) that is based on permanent magnets and has several advantages over the conventional ZS. We present the performances of the apparatus for two different magnet configurations: the \emph{dipole} and \emph{Halbach} configurations. The second part is about scattering experiments of guided matter waves on a complex potential. After describing the experimental setup that produces Bose-Einstein condensates in a crossed dipole trap, we report on three experiments. The first experiment studies the scattering of a matter wave on a finite size optical lattice that forms a Bragg reflector. We discuss the processes involved in the scattering and we study in detail the transmissivity across the Bragg mirror. We then demonstrate the trapping of a propagating Bose-Einstein condensate in a Bragg cavity that originates from the envelope of the lattice. We observe oscillations inside the cavity and partial tunneling out of the cavity for narrow classes of velocity. This technique allows to characterize new types of tunnel barriers in position space equivalent to submicronic repulsive barriers. Finally, we study the scattering of matter waves on an amplitude-modulated optical lattice, and analyse the transmissivity across this structure when varying the modulation frequency. We describe the complex dynamics at play within the Floquet-Bloch framework and the use of this technique to realize a new type of tunable velocity filter. This filter does not rely on any specific internal state configuratio

Zeeman slowers made simple with permanent magnets in a Halbach configuration

We describe a simple Zeeman slower design using permanent magnets. Contrary to common wire-wound setups no electric power and water cooling are required. In addition, the whole system can be assembled and disassembled at will. The magnetic field is however transverse to the atomic motion and an extra repumper laser is necessary. A Halbach configuration of the magnets produces a high quality magnetic field and no further adjustment is needed. After optimization of the laser parameters, the apparatus produces an intense beam of slow and cold 87Rb atoms. With a typical flux of 1 - 5 \times 10^10 atoms/s at 30 ms^-1, our apparatus efficiently loads a large magneto-optical trap with more than 10^10 atoms in one second, which is an ideal starting point for degenerate quantum gases experiments.Comment: 8+6 pages (article + appendices: calculation details, probe and oven description, pictures), 18 figures, supplementary material (movie, Mathematica programs and technical drawings