Neutral Atom Interactions at Surfaces, in Mixtures and Bose-Condensates

Abstract

This thesis presents, through a series of experimental and numerical results, an investigation of the collisional interactions of neutral atoms for topics of technological and scientific interest, namely, atom-surface interactions for lithography, and atom-atom interactions in cold atomic mixtures and Bose-Einstein condensates.<br /> In the first chapter I report on an experimental scheme to investigate the interaction of metastable helium atoms with molecular surface monolayers, which act as ultrathin resists for atom lithography. We seek to isolate the interaction between the metastable atom and the monolayer from other possible interactions, such as that of ultraviolet photons, which are also present in significant quantities. Using the characterized properties of a new liquid nitrogen-cooled discharge source, an experimental scheme was implemented which utilizes magnetic manipulation techniques for neutral atoms to create a lithography exposure involving metastable helium atoms alone.<br /> In the second chapter, the development of an experiment for the study of ultracold interactions between rubidium and cesium atoms is documented. Starting with an experiment for the Bose-Einstein condensation of Rb-87, modifications were made which allowed the simultaneous confinement of rubidium and cesium atoms in magneto-optical, quadrupole, and Ioffe trapping configurations. By imprinting a temperature gradient between the overlapped atomic clouds through optical molasses, re-thermalization between magnetically trapped rubidium and cesium atoms through <i>s</i>- and <i>p</i>-wave collisions was observed. In order to create precise and variable temperature gradients in the binary mixture, a modular 6.83 GHz source was implemented for species-selective evaporative cooling at the hyperfine transition frequency of rubidium. Bose-Einstein condensates of rubidium was created and the lifetime-limiting losses due to three-body collisions investigated. <br /> The third chapter puts forward the results of numerical simulations on the creation and propagation of bright soliton trains in Bose-condensates, based on the experimental observation of soliton trains by Strecker <i>et al.</i> (Nature <b>417</b>, 150 (2002)). Using a mean-field approach, numerical solutions of the Gross-Pitaevski equation were obtained which reproduce the key features of the experiment and offer insights into soliton collisions and the determination of soliton number.