Imaging Bose-Einstein condensates at ultra-low atom-numbers and time averaged adiabatic potentials

Abstract

Imaging Bose-Einstein Condensates at Ultra-Low Atom-Numbers and Time-Averaged Adiabatic Potentials Melina Pappa A thesis presented for the degree of Doctor of Philosophy Physics Department University of Crete FORTH IESL June 2011 This thesis presents theoretical principles on laser cooling and trapping as well as magnetic trapping and evaporative cooling, methods necessary for Bose-Einstein condensation. It presents the construction of a very dependable BEC machine. We demonstrate a novel class of trapping potentials, time-averaged adiabatic potentials (TAAP) which allows the generation of a large variety of traps and waveguides for ultracold atoms. The ring-geometry is of particular interest for guided matter-wave interferometry as it provides a perfectly smooth waveguide of controllable diameter, and thus a tunable sensitivity of the interferometer. In addition we report the experimental realization of double-well traps based on TAAP traps. Quantum degenerate Fermi gases and Bose-Einstein condensates give access to a vast new class of quantum states. The resulting multi-particle correlations places extreme demands on the detection schemes. Here we introduce diffractive darkground imaging as a novel ultra-sensitive imaging technique. We detect clouds with less than 30 atoms with near atom shot-noise limited signal to noise ratio. This presents an improvement of about one order of magnitude when compared to our standard absorption imaging. We also examine the optimal conditions for absorption imaging including saturation and fluorescence contributions.