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dc.contributor.advisorBradley, Ashton
dc.contributor.authorRooney, Samuel James
dc.date.available2012-11-01T21:00:13Z
dc.date.copyright2012
dc.identifier.citationRooney, S. J. (2012). C-field description of the quasi-equilibrium Bose gas: Persistent currents and kelvon-induced vortex decay (Thesis, Master of Science). University of Otago. Retrieved from http://hdl.handle.net/10523/2538en
dc.identifier.urihttp://hdl.handle.net/10523/2538
dc.description.abstractRecent experiments at the University of Arizona have demonstrated superb control and imaging of flattened superfluids revealing a rich landscape of vortex dynamics. Vortex dipoles have been created and their dynamics observed [Neely et al. Phys. Rev. Lett. 104, 160410 (2010)], and highly charged persistent currents have been formed through a clever combination of stirring and dissipation [T. W. Neely, PhD thesis, (2010)]. Many ultra-cold gas systems, including these, are in a regime that we may characterize as quasi-equilibrium: despite some external forcing, a large fraction of the gas remains in thermal equilibrium. In this thesis we use the stochastic projected Gross-Pitaevskii equation (SPGPE) to make quantitative predictions of the quasi-equilibrium Bose gas. We quantitatively compare the SPGPE with experiment by modeling the persistent current formation experiment performed at the University of Arizona [T. W. Neely, PhD thesis, (2010)]. We determine all SPGPE parameters for the toroidal system prior to simulation, enabling quantitative modeling of the experiment with no fitting parameters, giving a true test of the SPGPE theory. We find the SPGPE gives quantitative agreement with experiment, accurately predicting the size of the persistent current as well as the decay time of the vortices. We also observe the crucial role that thermal fluctuations have on enabling this agreement, showing the comprehensive SPGPE treatment is necessary to make quantitatively accurate calculations of quasi-equilibrium systems. This is the first quantitative agreement with experimental observations of vortex dynamics obtained with a theory of dissipation from first principles using no fitting parameters. We then systematically study the Kelvin mode excitations on a vortex line in a three dimensional Bose-Einstein condensate using the SPGPE. We give a quantitative measure of the magnitude of vortex bending caused by the activation of Kelvin modes, and find that vortex bending can be suppressed by tightening the confinement along the direction of the vortex line. This leads to a strong suppression of the vortex decay rate as the system enters a regime of two-dimensional vortex dynamics, characterized by a critical oblateness. In our final application of the SPGPE we simulate the decay of a vortex dipole. We model a recent experiment of Neely et al. [Neely et al. Phys. Rev. Lett. 104, 160410 (2010)], finding the SPGPE predicts a dipole lifetime consistent with experimental observations. We also show the experiment lies in the two-dimensional regime of vortex dynamics, validating our critical oblateness calculation.
dc.format.mimetypeapplication/pdf
dc.language.isoen
dc.publisherUniversity of Otago
dc.rightsAll items in OUR Archive are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.
dc.subjectBose-Einstein condensates
dc.subjectVortex dynamics
dc.titleC-field description of the quasi-equilibrium Bose gas: Persistent currents and kelvon-induced vortex decay
dc.typeThesis
dc.date.updated2012-11-01T20:23:15Z
dc.language.rfc3066en
thesis.degree.disciplinePhysics
thesis.degree.nameMaster of Science
thesis.degree.grantorUniversity of Otago
thesis.degree.levelMasters
otago.openaccessOpen
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