The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Dissertation for the degree of Doctor of Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Auditorium S1 at Helsinki University of Technology (Espoo, Finland) on the 14th of November, 2003, at 12 o'clock noon.
Overview in PDF format (ISBN 951-22-6854-X) [1137 KB]
Dissertation is also available in print (ISBN 951-22-6799-3)
After the experimental realization of Bose-Einstein condensation in dilute gases of alkali atoms, experimentalists started to trap the fermionic isotopes. The degenerate state for fermions was reported in 1999. The main objective of these experiments is to obtain superfluidity of fermionic gases. When there are attractive interactions between the fermions, the Fermi sea becomes unstable with respect to the formation of atomic Cooper pairs and the system becomes a superfluid. It turns out that the existing experimental cooling techniques allow minimum temperatures for fermions of the order of the Fermi temperature. Using Feshbach resonances induced by magnetic fields enhances the effective interactions between the atoms leading to superfluid transition temperatures of the order of the Fermi energy. This is a completely new regime of fermionic superfluidity far from the BCS superconductors, 3He and even high-Tc superconductors. The achievement of superfluidity on gases of fermionic alkalis is currently being pursued in many experimental groups.
In this thesis, different signatures of the superfluid transition have been considered. The use of almost on-resonant laser light for coupling between the different internal states of the atoms as a method for probing superfluidity has been analyzed. Coupling between the paired states has been proposed as a way to directly detect the Cooper pair size. The Josephson effect, related to the phases of two coupled superfluids, is shown to present an asymmetry when the internal states of the atoms forming the pairs are coupled with different detunings. Vortices, intimately related to superfluidity, have also been considered. The single vortex solution of the Ginzburg-Landau equation for the superfluid order parameter has been numerically computed and a new vortex core size reflecting the trapping geometry has been obtained. Bloch oscillations have been analyzed for fermionic atoms both in the degenerate regime and in the superfluid regime. Superfluidity is found to supress the amplitude of the Bloch oscillations.
This thesis consists of an overview and of the following 6 publications:
Keywords: superfluidity, Fermi gases, quantum gases, Bose-Einstein condensation, vortices
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© 2003 Helsinki University of Technology