The experimental realisation of Bose-Einstein condensation in 1995 opened up a wealth of opportunities for probing quantum states of matter. The development of many tools used to manipulate such ultracold samples and the rapid progress on understanding these systems will ultimately lead to great technological advances. The work described in this thesis contributes to this worldwide effort and here we present experiments which investigate the properties and behaviour of ultracold atoms.
In the first experiments presented here, we have studied features of Bose-Einstein condensates loaded into an optical lattice formed by the interference of two laser beams. By altering the phase of the lattice at the Bragg condition, we investigate the effect of the phase shift on the dressed-atom states. We find that by applying a +(-)[pi]/2 phase shift after a [pi]/2 (3[pi]/2) lattice pulse, we are able to quickly and precisely load the ground and first excited eigenstates of the lattice. In another experiment, we use a periodically pulsed stationary optical lattice and a tightly-confined Bose-Einstein condensate to investigate the nonlinear kicked harmonic oscillator at quantum anti-resonance. We observe periodic behaviour in the energy of the condensate, however we show that the nonlinearity is not strong enough to enter the predicted chaotic regime. In addition, the amplitude of the energy oscillations damps to an average value and we relate this to dephasing of the coupling across the finite momentum width of the condensate.
In the second series of experiments, we use a double-well magnetic collider to investigate cold collisions between ultracold atoms. By creating two ultracold clouds in a double-well magnetic trap and then transforming the trap to a single well, we accelerate the clouds together to initiate a collision between them. We describe in detail the analysis method that we use to extract the partial-wave phase shifts from the matter-wave interference patterns associated with the scattered atoms. We then implement a two-photon pulse, which is applied prior to the collision to convert one of the clouds to a different spin state. This enables the study of scattering between distinguishable states which exhibited anti-symmetric p-wave scattering via the interference with the s- and d-waves previously observed for indistinguishable states. We find the position of the d-wave shape resonance and compare our data to a coupled-channels model.
| Identifer | oai:union.ndltd.org:ADTP/217444 |
| Date | January 2006 |
| Creators | Mellish, Angela Susan, n/a |
| Publisher | University of Otago. Department of Physics |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Angela Susan Mellish |
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