This dissertation presents several experimental methods that were devised to generate or manipulate quantized vortices in highly oblate dilute-gas Bose-Einstein condensates (BECs). Studies that involve single vortex dynamics, vortex-vortex interactions, and vortex-impurity interactions are essential in developing a deeper understanding of the nature of superfluidity and in particular, superfluid turbulence. In highly oblate systems, vortex dynamics have a two-dimensional (2D) nature and the resulting superfluid characteristics may be substantially different from those in three-dimensional (3D) superfluids. However, there have been remarkably few experimental studies of 2D vortex dynamics in superfluids. Therefore, to study 2D vortex dynamics and interactions, it is necessary to first develop experimental methods that can generate vortices and vortex distributions in nominally 2D systems, such as highly oblate BECs. Four main experiments are discussed in this dissertation. Two of these experiments generate multiple singly quantized vortices in a relatively stochastic manner leading to disordered vortex distributions. From these two vortex methods, the physics of high vorticity and highly disordered systems may be observed and studied in a highly oblate system. These methods may prove useful in studies of 2D quantum turbulence. The other two experiments involve newly developed techniques for controlled generation and manipulation of vortices. One of these methods creates multiply quantized pinned vortices with a control in the generated vorticity. The other method reliably creates a pair of singly quantized vortices of opposite circulation, whose positions can be easily manipulated after creation, such that they can be placed in any location within the BEC. The two techniques may be scalable to higher number of vortices and may prove useful in superfluid dynamics and vortex interactions that require repeatable vortex distributions. Taken together, these tools and methods may be applicable to many further studies of vortex physics in highly oblate BECs.

The density amplitude of an isolated quantum vortex line in superfluid 4He is calculated using a generalized Gross-Pitaevskii (G-P) equation. The generalized G-P equation for the order parameter extends the usual mean-field approach by replacing the interatomic potential in the ordinary G-P equation by a local, static T matrix, which takes correlations between the particles into account. The T matrix is a sum of ladder diagrams appearing in a diagrammatic expansion of the mean field term in an exact equation for the order parameter. It is an effective interaction which is much softer than the realistic interatomic Morse dipole-dipole potential from which it is calculated. A numerical solution of the generalized G-P equation is required since it is a nonlinear integro-differential equation with infinite limits. For the energy denominator in the T matrix equation, a free-particle spectrum and the observed phonon-roton spectrum are each used. For the fraction of particles in the zero-momentum state (Bose-Einstein dondensate) which enters the equation, both a theoretical value of 0.1 and an experimental value of 0.024 are used. The chemical potential is adjusted so that the density as a function of distance from the vortex core approaches the bulk density asymptotically. Solutions of the generalized G-P equation are not very dependent on the choice of energy denominator or condensate fraction. The density profile is a monotonically increasing function of the distance from the vortex core. The core radius, defined to be the distance to half the bulk density, varies from 3.7 A to 4.7 A, which is over three times the experimental value of 1.14 A at absolute zero.

No presente trabalho, estudamos o comportamento de um Condensado de Bose-Einstein contendo um vórtice tipo linha aprisionado, e durante o vôo livre. Desta maneira foi feito a analise da velocidade de expansão do aspect ratio da nuvem para três formatos de armadilhas, as quais são potenciais harmônicos sem rotação, incluindo a comparação entre a velocidade de expansão do raio da nuvem e do núcleo do vórtice. Vimos que a precessão do vórtice pode independer de um potencial com rotação, sendo diretamente relacionada com a densidade da nuvem atômica. Ao supor um Condensado com um vórtice não-fundamental e estável obtemos uma possível descrição do aspect ratio da nuvem, como uma aproximação para uma rede de vórtices; utilizando apenas de um método semi-analítico. / In this work, we have studied the behavior of a Bose-Einstein Condensate contend a line vortex at trap, and while the free flight. In this way it was analysed the expansion speed of clouds aspect ratio into three kind of traps, which are non-rotating harmonic potentials, including the comparation between velocity of the radius and the vortex core under expansion. We have seem the vortexs precession may be independent of a rotating potential, thus it is directly associated with the density profile of atomic cloud. By assuming a Condensate within a stable non-funtamental vortex we obtain a possible description of aspect ratio of cloud, like an approach for a lattice vortex; using only a semi-analytic method.

No presente trabalho, estudamos o comportamento de um Condensado de Bose-Einstein contendo um vórtice tipo linha aprisionado, e durante o vôo livre. Desta maneira foi feito a analise da velocidade de expansão do aspect ratio da nuvem para três formatos de armadilhas, as quais são potenciais harmônicos sem rotação, incluindo a comparação entre a velocidade de expansão do raio da nuvem e do núcleo do vórtice. Vimos que a precessão do vórtice pode independer de um potencial com rotação, sendo diretamente relacionada com a densidade da nuvem atômica. Ao supor um Condensado com um vórtice não-fundamental e estável obtemos uma possível descrição do aspect ratio da nuvem, como uma aproximação para uma rede de vórtices; utilizando apenas de um método semi-analítico. / In this work, we have studied the behavior of a Bose-Einstein Condensate contend a line vortex at trap, and while the free flight. In this way it was analysed the expansion speed of clouds aspect ratio into three kind of traps, which are non-rotating harmonic potentials, including the comparation between velocity of the radius and the vortex core under expansion. We have seem the vortexs precession may be independent of a rotating potential, thus it is directly associated with the density profile of atomic cloud. By assuming a Condensate within a stable non-funtamental vortex we obtain a possible description of aspect ratio of cloud, like an approach for a lattice vortex; using only a semi-analytic method.