All-optical 87Rb Bose-Einstein condensate apparatus: construction and operation

Humbert, I. L. H. (2012). All-optical 87Rb Bose-Einstein condensate apparatus: construction and operation PhD Thesis, School of Mathematics and Physics, The University of Queensland.

       
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Author Humbert, I. L. H.
Thesis Title All-optical 87Rb Bose-Einstein condensate apparatus: construction and operation
Formatted title
All-optical 87Rb Bose-Einstein condensate apparatus: construction and operation
School, Centre or Institute School of Mathematics and Physics
Institution The University of Queensland
Publication date 2012
Thesis type PhD Thesis
Supervisor Halina Rubinzstein-Dunlop
Norman Heckenberg
Mark Baker
Total pages 192
Total colour pages 81
Total black and white pages 111
Language eng
Subjects 0206 Quantum Physics
Formatted abstract
Research on degenerate quantum gases of dilute atomic gases has become a well established field in modern physics and revealed many astonishing phenomena. The first experiments on Bose and Fermi gases at low temperatures aimed to prove the predictions of quantum mechanics on a macroscopic scale. Since then we make use of Bose and Fermi gases and mixtures of any combination to model other many body systems. A property of Bose Einstein condensates is superfluidity which we want to investigate further in toroidal potentials with a new apparatus which can produce an all-optical BEC. This means trapping thermal atoms in an optical dipole trap and cooling the sample by evaporation into the quantum degenerate regime. This new technique was first successfully demonstrated by M.D. Barrett et al. in 2001 and promises to be faster and simpler than the well established and common way of evaporation in magnetic traps.
A new apparatus was built by the author and we report on the experimental details of the trapping of 87Rb atoms from a hot vapour and cooling them in a magneto-optical trap, and further evaporation to quantum degeneracy in a crossed optical dipole trap operating at a wavelength of λ = 1064nm, with accurate control of the power in both beams via a feedback loop. The evaporation of neutral atoms of 87Rb in far red detuned optical dipole traps using linearly polarised laser light is spin independent, and mixed spinor condensates of the F=1 manifold can be formed. As an empirical technique we found by applying a magnetic gradient field during the final evaporation that we can selectively populate mF spin states or prepare mixtures. This intriguing mechanism was found earlier as well by M. S. Chang, but is yet not fully understood and subject of our future research. We can now routinely prepare an almost pure condensate containing up to 7000 atoms in the condensed phase purely in the mF = 0 spin state.
This thesis contains the theoretical framework of Bose-Einstein condensation with in mean-field theory, the concepts of cooling of atoms in magneto-optical traps, the trapping and evaporation in optical dipole traps and the experimental realisation. In the future this experiment will be extended by a fast scanning dipole trap to apply arbitrary time averaged potentials of more complex geometries, such as toroidal traps to study the effects of superfluidity in a periodic potential. The production of toroidal traps and cold atoms in such a trap are outlined in this thesis.
Keyword Bose-Einstein condensate
Optical trapping

 
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