Spatially selective Bragg scattering: a signature for vortices in Bose-Einstein condensates

We demonstrate that Bragg scattering from a condensate can be sensitive to the spatial phase distribution of the initial state. This allows preferential scattering from a selected spatial region, and provides a robust signature for a vortex state. We develop an analytic model which accurately describes this phenomenon and we give quantitative predictions for current experimental conditions.Comment: 5 pages, 3 figure

Contagious Discourse: Germs, Mass Media, and the Shaping of Reality

Over the past two decades, mass media coverage of certain infectious diseases has become more abundant. News reports of many of these contagious illnesses invoke fear in many people, such as Ebola and pandemic influenza; multidrug-resistant strains of infectious diseases, such as tuberculosis; and agents of biological warfare, a concern that is now at the forefront with many Americans due to the most recent act of bioterrorism on American soil following the events of September 11th. This dissertation focuses on the American public\u27s perception of infectious diseases, particularly as portrayed in the cultural science curriculum. I examine the cyclic nature of the discourse of contagion and its consequences. In doing so, I present a critical analysis of who controls what is included in the discourse, how agendas contribute to what is considered important, and how various threads of the discourse intertwine to create a gestalt-like complex. With this controlled discourse in mind, I discuss how experiencing the conversation contributes to what people believe about the threat of contagion and present how these assumptions shape our perception of reality. Lastly, I demonstrate how our altered perception of reality leads to behavioral changes that alter our world. To illustrate this, I provide examples of two types of reality shifts that occurred over the past few decades: the increase in commercial antibacterial products and antibiotic use contributed to the development of antibiotic-resistant bacterial strains (a biological shift), and the fear of weapons of mass destruction lead to increased support for a war against Iraq (a sociological shift)

Quantum kinetic theory VII: The influence of vapor dynamics on condensate growth

We extend earlier models of the growth of a Bose-Einstein condensate to include the full dynamical effects of the thermal cloud by numerically solving a modified quantum Boltzmann equation. We determine the regime in which the assumptions of the simple model are a reasonable approximation, and compare our new results with those that were earlier compared with experimental data. We find good agreement with our earlier modelling, except at higher condensate fractions, for which a significant speedup is found. We also investigate the effect of temperature on condensate growth, and find that this has a surprisingly small effect. The discrepancy between theory and experiment remains, since the speedup found in these computations does not occur in the parameter regime specified in the the experiment.Comment: Fourteen pages, TeX source with 11 figures. Changes : Extended section on formalism to include a derivation of the ergodic Boltzmann equation that we use, and a fuller explanation of the numerical methods. Explained more fully the possible errors with the experimental data. Added section detailing the source of possible errors in this formulation. Added comparison of our work with the manuscript cond-mat/0001323, and some analysis of the fits to the MIT growth curve

Bragg spectroscopy of an accelerating condensate with solitary-wave behaviour

We present a theoretical treatment of Bragg spectroscopy of an accelerating condensate in a solitary-wave state. Our treatment is based on the Gross-Pitaevskii equation with an optical potential representing the Bragg pulse and an additional external time-dependent potential generating the solitary-wave behaviour. By transforming to a frame translating with the condensate, we derive an approximate set of equations that can be readily solved to generate approximate Bragg spectra. Our analytic method is accurate within a well defined parameter regime and provides physical insight into the structure of the spectra. We illustrate our formalism using the example of Bragg spectroscopy of a condensate in a time-averaged orbiting potential trap.Comment: 9 pages, 3 figure

Stabilizing an atom laser using spatially selective pumping and feedback

We perform a comprehensive study of stability of a pumped atom laser in the presence of pumping, damping and outcoupling. We also introduce a realistic feedback scheme to improve stability by extracting energy from the condensate and determine its effectiveness. We find that while the feedback scheme is highly efficient in reducing condensate fluctuations, it usually does not alter the stability class of a particular set of pumping, damping and outcoupling parameters.Comment: 7 figure