Gaz de Fermi en interaction forte: Du condensat de molécules aux paires de Cooper

Abstract : This thesis presents properties of a strongly interacting
quantum-degenerate Fermi gas. First, we study theoretically the limit
to the cooling of a Fermi gas due to atom losses. A fermionic \lif gas
is then studied in the vicinity of a s-wave Feshbach resonance. By
adjusting the magnetic field, one can control the sign and the
strength of the effective atom-atom interactions. We demonstrate the
efficient formation of weakly bound molecules, which are composed of
two fermions. These results are interpreted using a model assuming
thermodynamic equilibrium between atoms and molecules. Due to the
Pauli principle, these molecules are extraordinarily stable near the
resonance peak. This property allows us to produce a molecular
Bose-Einstein condensate (BEC) and to measure the mean field
interaction energy between molecules. When increasing the magnetic
field over the Feshbach resonance, one expects a phase transition at
low temperature similar to the BCS (Bardeen, Cooper, Schrieffer)
superconducting transition in metals. Close to resonance the gas is a
strongly interacting N-body system, difficult to treat theoretically.
Experimentally, we studied the expansion of the gas in this transition
region between a molecular condensate and a BCS phase. Finally we
characterized losses in the vicinity of p-wave Feshbach resonances.
Document type :
Theses
Atomic Physics [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 2004. French


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Submitted on : Thursday, January 27, 2005 - 4:07:14 PM
Last modification on : Friday, January 20, 2006 - 5:24:13 PM

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Thomas Bourdel. Gaz de Fermi en interaction forte: Du condensat de molécules aux paires de Cooper. Atomic Physics [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 2004. French. <tel-00008271>

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