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Superfluidity in Fermi Gases

Final Activity Report Summary - SUPERFLUIDFERMIGAS 2 (Superfluidity in Fermi Gases)

The subject of our proposal was the study of superfluidity in an ultracold gas of fermionic atoms. Superfluidity is a quantum phenomenon closely related to superconductivity, in which a fluid flows without resistance. The most prominent example is liquid helium, but in recent years ultracold atomic gases have emerged as a new type of superfluid. Fermions are particles, such as electrons and some atoms, with half-integer spin and, during the last three to four years it became possible to form a superfluid in ultracold gases of interacting fermionic atoms. The most exciting links between these atomic gases and condensed matter physics are for fermions, since it is possible to create systems which correspond almost perfectly to important theoretical models. This could bring new understanding to areas such as high-temperature superconductivity, a phenomenon with enormous technological implications.

During the time of the fellowship we used expansion measurements to investigate the properties and superfluid character of ultracold fermionic lithium. The gas was prepared in the strongly interacting regime with tuneable interactions, a unique and crucial feature of quantum gas experiments. Via releasing the gas from its trap under various conditions and analysing the dynamics of the expansion, we were able to test theoretical models describing this quantum many-body system. More specifically, we were able to characterise the momentum distribution of the gas in different regimes of atomic interactions and we saw evidence for a breakdown of superfluidity in the limit of weak attraction. We also undertook an upgrade of almost the entire experimental apparatus, enabling a whole series of new experiments in 2007 and beyond, including fermionic superfluidity in periodic potentials.