Exotic superfluid states of ultra-cold Fermi gases

This is a study of ultra-cold Fermi gases in different systems. This thesis is focused on exotic superfluid states, for an example on the three component Fermi gas and the FFLO phase in optical lattices. In the two-components case, superfluidity is studied mainly in the case of the spin population imbalanced Fermi gases and the phase diagrams are calculated from the mean-field theory. Different methods to detect different phases in optical lattices are suggested. In the three-component case, we studied also the uniform gas and harmonically trapped system. In this case, the BCS theory is generalized to three-component gases. It is also discussed how to achieve the conditions to get an SU(3)-symmetric Hamiltonian in optical lattices. The thesis is divided in chapters as follows: Chapter 1 is an introduction to the field of cold quantum gases. In chapter 2 optical lattices and their experimental characteristics are discussed. Chapter 3 deals with two-components Fermi gases in optical lattices and the paired states in lattices. In chapter 4 three-component Fermi gases with and without a harmonic trap are explored, and the pairing mechanisms are studied. In this chapter, we also discuss three-component Fermi gases in optical lattices. Chapter 5 devoted to the higher order correlations, and what they can tell about the paired states. Chapter 6 concludes the thesis.

Tässä väitöksessä tutkitaan ultrakylkien fermikaasujen suprajuoksevuutta. Työssä on keskitytty eksoottisiin suprjuokseviin tiloihin, kuten kolmikomponentiseen fermikaasuun ja FFLO-faasiin optisissa hiloissa. Kaksikomponenttisen fermikaasun tapauksessa, olemme keskittyneet lähinnä spinpopulaatioepätasapainoisiin fermikaasuihin, ja laskemme faasidiagrammit käyttäen keskeiskenttä approksimaatiota. Erillaisia metodeja havaita erillaiset faasit esitetään. Tutkimme myös kolmikomponenttista fermikaasua loukussa ja ilman loukkua. Kolmikomponenttisessa tapauksessa standardia BCS-teoriaa on yleistetty. Työssä on tutkittu myös kuinka saavuttaa SU(3)-symmetria optisissa hiloissa.