Topological defects and phase transitions in dilute Bose gases

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Informaatio- ja luonnontieteiden tiedekunta | Doctoral thesis (article-based)
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Date
2010
Major/Subject
Mcode
Degree programme
Language
en
Pages
Verkkokirja (2086 KB, 68 s.)
Series
Dissertations of Department of Applied Physics, 160
Abstract
Since the discovery of Bose-Einstein condensation in dilute atomic vapours in 1995, there has been a monumental increase in the research effort in the field of atomic physics due to the unforeseen opportunities and challenges that the degenerate quantum gases present. In particular, quantum gases can emulate complicated models that arise in solid state and high energy physics, allowing realisations of exotic phenomena that have proven to be elusive in their original context. An outstanding example is the existence of various topological defects in degenerate quantum gases with internal degrees of freedom. Topological excitations such as skyrmions and several types of monopoles can be shown to take place in Bose gases with a hyperfine spin degree of freedom as a result of a coupling to an external field or due to thermal fluctuations. A central question in the context of dilute Bose gases is the relation between superfluidity and Bose-Einstein condensation. The dimensionality of the underlying space as well as the internal degrees of freedom have a direct impact on the existence and the nature of the Bose-Einstein condensate. For example, any uniform Bose gas in two spatial dimensions or an antiferromagnetic spinor Bose gas can give rise to a superfluid state which does not involve a conventional Bose-Einstein condensate corresponding to a single macroscopically occupied quantum state. In this Thesis, properties of different topological defects and their relation to superfluidity in dilute Bose gases are investigated. Stability and creation of coreless vortices are first studied and a method to cyclically increase the angular momentum of the condensate is introduced. Subsequently, the properties and creation of different types of monopoles are investigated and an experimentally feasible method to create a Dirac monopole is presented. Finally, finite temperature phase transitions in quasi-two-dimensional Bose gases with a spin degree of freedom are analysed and, as a related subject, the stability of vortex clusters formed by vortices and antivortices is studied.
Description
Supervising professor
Nieminen, Risto, Prof.
Thesis advisor
Möttönen, Mikko, Dr.
Keywords
Bose-Einstein condensation, surpefluidity, vortex, phase transitions
Other note
Parts
  • [Publication 1]: M. Takahashi, V. Pietilä, M. Möttönen, T. Mizushima, and K. Machida. 2009. Vortex-splitting and phase-separating instabilities of coreless vortices in F=1 spinor Bose-Einstein condensates. Physical Review A, volume 79, number 2, 023618, 10 pages. © 2009 American Physical Society (APS). By permission.
  • [Publication 2]: Ville Pietilä, Mikko Möttönen, and Mikio Nakahara. 2008. Topological vortex creation in spinor Bose-Einstein condensates. In: E. O. Kamenetskii (editor). Electromagnetic, Magnetostatic, and Exchange-Interaction Vortices in Confined Magnetic Structures. Kerala, India: Research Signpost, pages 297-329. ISBN 978-81-7895-373-1.
  • [Publication 3]: Mikko Möttönen, Ville Pietilä, and Sami M. M. Virtanen. 2007. Vortex pump for dilute Bose-Einstein condensates. Physical Review Letters, volume 99, number 25, 250406, 4 pages. © 2007 American Physical Society (APS). By permission.
  • [Publication 4]: V. Pietilä, M. Möttönen, and S. M. M. Virtanen. 2007. Stability of coreless vortices in ferromagnetic spinor Bose-Einstein condensates. Physical Review A, volume 76, number 2, 023610, 7 pages. © 2007 American Physical Society (APS). By permission.
  • [Publication 5]: J. A. M. Huhtamäki, M. Möttönen, T. Isoshima, V. Pietilä, and S. M. M. Virtanen. 2006. Splitting times of doubly quantized vortices in dilute Bose-Einstein condensates. Physical Review Letters, volume 97, number 11, 110406, 4 pages. © 2006 American Physical Society (APS). By permission.
  • [Publication 6]: Ville Pietilä and Mikko Möttönen. 2009. Creation of Dirac monopoles in spinor Bose-Einstein condensates. Physical Review Letters, volume 103, number 3, 030401, 4 pages. © 2009 American Physical Society (APS). By permission.
  • [Publication 7]: Ville Pietilä and Mikko Möttönen. 2009. Non-Abelian magnetic monopole in a Bose-Einstein condensate. Physical Review Letters, volume 102, number 8, 080403, 4 pages. © 2009 American Physical Society (APS). By permission.
  • [Publication 8]: V. Pietilä, M. Möttönen, T. Isoshima, J. A. M. Huhtamäki, and S. M. M. Virtanen. 2006. Stability and dynamics of vortex clusters in nonrotated Bose-Einstein condensates. Physical Review A, volume 74, number 2, 023603, 6 pages. © 2006 American Physical Society (APS). By permission.
  • [Publication 9]: Ville Pietilä, Tapio P. Simula, and Mikko Möttönen. 2010. Finite-temperature phase transitions in quasi-two-dimensional spin-1 Bose gases. Physical Review A, volume 81, number 3, 033616, 8 pages. © 2010 American Physical Society (APS). By permission.
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