Bose-Einstein Condensates In Non-Harmonic Optical Potentials

Sebastian Schnelle (2011). Bose-Einstein Condensates In Non-Harmonic Optical Potentials PhD Thesis, School of Mathematics & Physics, The University of Queensland.

       
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Author Sebastian Schnelle
Thesis Title Bose-Einstein Condensates In Non-Harmonic Optical Potentials
School, Centre or Institute School of Mathematics & Physics
Institution The University of Queensland
Publication date 2011-03
Thesis type PhD Thesis
Supervisor Halina Rubinsztein-Dunlop
Norman Heckenberg
Erik van Ooijen
Total pages 131
Total colour pages 41
Total black and white pages 90
Language eng
Subjects 01 Mathematical Sciences
Abstract/Summary This thesis presents work on Bose-Einstein condensates in non-harmonic optical potentials. First, a new trap design developed at the University of Queensland is presented that allows the creation of nearly arbitrary two-dimensional potential landscapes by spatially scanning a far red-detuned laser beam using a two-dimensional acousto-optic modulator. In conjunction with a feed-forward technique this trap is capable of producing optical traps which have the necessary stability to be used in ultra-cold atom research. Different geometries are presented. In particular toroidal trap geometries are discussed which are interesting because they offer the possibility for a multiply connected Bose-Einstein condensate. The trap also offers the possibility of dynamic potentials which have been employed to measure the critical velocity of superfluidity in Bose-Einstein condensates. Secondly, measurements on condensation dynamics are presented which use an optical dimple potential superimposed upon a harmonic magnetic trap. In the experiments the dimple potential is ramped on slowly or turned on suddenly for a range of dimple depths and widths and the condensate fraction and temperature are measured as a function of hold times. The measurements taken are compared to equilibrium thermodynamics and quantum kinetic theory and for the first time a quantitative model is presented that allows correct prediction of condensate fractions and temperatures in good agreement with the measurements. Also presented are first results in condensate rethermalization experiments where a dimple potential is suddenly switched off and the condensate left to rethermalize in a much wider magnetic potential. The measurements show a sudden breakdown in condensate fraction followed by a subsequent recovery. So far no theory exists to properly interpret the results as quantum kinetic theory cannot be applied to the problem. Lastly, progress on experiments to measure the critical velocity of superfluidity in Bose-Einstein condensates is reported. Calculations have been carried out that show the creation of solitons and vortices as mechanisms to dissipate energy leading to a breakdown of superfluid behaviour at velocities lower than that predicted by Landau’s theory of superfluidity, the first theory to describe superfluidity. Progress on an experiment is presented that uses the scanning beam trap developed as part of this project to create a line potential with a moving barrier to measure the critical velocity and show solitons and vortices as the mechanisms for energy dissipation as seen in the calculations.
Keyword Bose-einstein Condensate
Optical trapping
Additional Notes 37, 39-42, 44-51, 59, 62-63, 66, 69, 72, 75, 86-91, 99, 102-105, 109, 111-119

 
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