Making a spin-difference in quantum gases

Miikka Heikkinen

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

This thesis studies the theory of quantum gases. We focus on fermionic superfluidity in systems in which the control over the spin degree of freedom has a central role. We explain the microscopic origin of the spin-asymmetric Josephon effect, and propose methods for realizing this effect experimentally in quantum gases. We investigate the phenomenon of fermionic superfluidity in the presence of spin-polarization, with our main focus on the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) phase. We show that the FFLO pairing mechanism leads to an anisotropic speed of sound which can be used to identify the state in experiments. Using real-space dynamical mean field theory (DMFT), we compute the phase diagram of a trapped, spin-polarized Fermi gas in a dimensional crossover from a 1D to a 3D optical lattice. We find that the FFLO state is realized in a broad region of parameters throughout the crossover while the shell structure of the Fermi gas preceding the transition to the full FFLO state shows a strong dependence on the dimensionality. Finally, we utilize the cluster DMFT method to show that the FFLO state is stable against non-local quantum fluctuations even though these fluctuations do affect the critical temperature of the state.
Translated title of the contributionSpin-asymmetria kvanttikaasuissa
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Törmä, Päivi, Supervising Professor
  • Törmä, Päivi, Thesis Advisor
Publisher
Print ISBNs978-952-60-5708-8
Electronic ISBNs978-952-60-5709-5
Publication statusPublished - 2014
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • quantum gases
  • superfluidity
  • optical lattice
  • Hubbard model
  • Josephson effect
  • Fulde-Ferrell-Larkin-Ovchinnikov phase
  • generalized random-phase approximation
  • dynamical mean-field theory

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