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Ultracold Fermi gases : next generation experiment and impurity physics

Abstract : Part of the thesis concerns the description of a new generation experiment built within the ultra-cold fermion gas team at the Kastler Brossel laboratory. The experimental steps that lead to the realization and characterization of a fermionic superfluid are described along with the physical principles behind these methods, which are well established in the field. The second part deals with two theoretical studies concerning the physics of an impurity. When an impurity enters an interacting medium, its energy exhibits logarithmic divergences in its perturbative development. We use the method of Green's functions to understand the fundamental processes at the origin of these divergences. For the second project, we study the phase diagram of an impurity submerged in a double Fermi sea without interactions. We use a variational method to show that there is a first degree phase transition between the limit of weak impurity-fermion interaction where a quasi-particle called the polaron is present, and the limit of stronger interaction where there is a bound state of three particles, called a trimer, close to the Fermi surface.
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Submitted on : Thursday, May 12, 2022 - 4:26:18 PM
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Ragheed Alhyder. Ultracold Fermi gases : next generation experiment and impurity physics. Quantum Physics [quant-ph]. Université Paris sciences et lettres, 2020. English. ⟨NNT : 2020UPSLE075⟩. ⟨tel-03666647⟩



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