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Title:  Properties of rotating ultracold bosonic quantum gases 
Author(s):  Baharian Khoshkhou, Soheil 
Director of Research:  Baym, Gordon A. 
Doctoral Committee Chair(s):  Ceperley, David M. 
Doctoral Committee Member(s):  Baym, Gordon A.; DeMarco, Brian L.; Stack, John D. 
Department / Program:  Physics 
Discipline:  Physics 
Degree Granting Institution:  University of Illinois at UrbanaChampaign 
Degree:  Ph.D. 
Genre:  Dissertation 
Subject(s):  BoseEinstein condensate
rotating superfluid vortex lattice strongly correlated state metastable current 
Abstract:  In this dissertation, we study rotational properties of ultracold bosonic quantum gases in two trapped configurations, a quasitwodimensional gas in a harmonic trap and a quasionedimensional gas in a toroidal trap. First, we investigate the effects of correlations on the properties of the ground state of the rotating harmonicallytrapped Bose gas by adding Bogoliubov fluctuations to the meanfield ground state of an Nparticle singlevortex system. We demonstrate that the fluctuationinduced correlations lower the energy compared to that of the meanfield ground state, that the vortex core is pushed slightly away from the center of the trap, and that an unstable mode with negative energy (for rotations slower than a critical frequency) emerges in the energy spectrum, thus, pointing to a better state for slow rotation. We construct meanfield ground states of 0, 1, and 2vortex states as a function of rotation rate and determine the critical frequencies for transitions between these states, as well as the critical frequency for appearance of a metastable state with an offcenter vortex and its image vortex in the evanescent tail of the cloud. Then, we show how the configurationspace form of the abovementioned Bogoliubov groundstate wave function of a bosonic condensate with a single vortex in a harmonic trap can be described in terms of bosonic Jastrow correlations. We then generalize this result to study the effects of such correlations on a meanfield vortex lattice state and show that the included correlations lower the energy below that of the meanfield state. Although the reduction is relatively small, it is a precursor of the more general expected effect of correlations in describing the melting of the vortex lattice at a high angular momentum per particle. Finally, we study the stability and dynamics of an ultracold bosonic gas trapped in a toroidal geometry and driven by rotation in the absence of dissipation. We first delineate, via the Bogoliubov mode expansion, the regions of stability and the nature of instabilities of the system for both repulsive and attractive interaction strengths. To study the response of the system to variations in the rotation rate, we introduce a “disorder” potential, breaking the rotational symmetry. We demonstrate the breakdown of adiabaticity as the rotation rate is slowly varied and find forced tunneling between the eigenstates of the system. The nonadiabaticity is signaled by the appearance of a swallowtail loop in the lowestenergy level, a general sign of hysteresis. Then, we show that this system is in onetoone correspondence with a trapped gas in a doublewell potential and thus exhibits macroscopic quantum selftrapping. Finally, we show that selftrapping is a direct manifestation of the behavior of the lowestenergy level. 
Issue Date:  20140116 
URI:  http://hdl.handle.net/2142/46831 
Rights Information:  Copyright 2013 Soheil Baharian Khoshkhou 
Date Available in IDEALS:  20140116 20160116 
Date Deposited:  201312 
This item appears in the following Collection(s)

Dissertations and Theses  Physics
Dissertations in Physics 
Graduate Dissertations and Theses at Illinois
Graduate Theses and Dissertations at Illinois