Non-perturbative collective properties of trapped ultracold atomic gases.
Item
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Title
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Non-perturbative collective properties of trapped ultracold atomic gases.
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Identifier
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AAI3232028
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identifier
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3232028
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Creator
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Kaurov, Vitaliy.
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Contributor
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Adviser: Anatoly Kuklov
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Date
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2006
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter | Physics, Atomic
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Abstract
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In this thesis two problems in the field of ultracold atomic gases are investigated: (1) Atomic Josephson vortex in quasi-1D double-waveguide containing one-component atomic superfluid; (2) Drag effect in strongly interacting two-component superfluid in optical lattice.;In the first problem quasi-one-dimensional long Bose-Josephson junction is considered. It consists of two parallel waveguides containing single-component atomic Bose-Einstein condensates coupled by tunneling. It is shown that such system supports atomic Josephson vortex (JV) - a soliton characterized by circulating atomic supercurrent. Exact stationary solution is found within mean field approach. Dynamics of the long Bose-Josephson junction is analyzed variationally and numerically. It is shown that upon increasing the Josephson coupling, the JV transforms spontaneously into a dark soliton and vice versa. This reversible interconversion has no analogy in higher spatial dimensions. Atomic JV can be controllably manipulated by imposing a tunneling bias current created by a difference of chemical potentials on the waveguides. This effect, which has its origin in the Berry phase structure of a vortex, is very robust in the whole range of the parameters where the JV exists. Acceleration of the JV up to a certain threshold speed, determined by the strength of the Josephson coupling, results in the phase slip causing switching of the vorticity. It is shown how the JV can be created by the phase imprinting technique and can be identified by a specific tangential feature in the interference picture produced by expanding clouds released from the waveguides. It is proposed that the JV can be utilized for controlled and coherent transfer of Bose-Einstein condensates and as a possible mobile qubit.;The second problem is devoted to investigating the mutual drag---non-dissipative coherent transfer of momentum from one component to another---in strongly interacting two-component superfluids in optical lattice (OL). While being analogous to the Andreev-Bashkin (AB) effect in the Galilean-invariant superfluid Helium, the drag in OL is shown to be drastically different due to breaking of the Galilean symmetry by OL. The combination of strong interaction and OL violates the AB relation of the drag coefficient to the effective mass of quasi-particles. In particular, this coefficient can change sign. Two competing drag mechanisms in OL are shown to be: the vacancy-assisted motion and proximity to a quasi-molecular state. Strong drag can radically change the structure of lowest energy topological excitation---vortex or persistent current. In contrast to the standard situation in a single-component superfluid, a vortex can become a composite object in which singular circulation of one component binds several circulation quanta of the other component. In the SQUID-type geometry, the circulation can become fractional. The analytical (within the Mean Field approach) and numerical (by the Monte Carlo Worm-Algorithm) results are presented. It is found that the Mean Field does not adequately describes all aspects of the drag effect in OL.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
