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Theses

Impurity immersed in a two-component Fermi gas

Abstract : The physics of strongly correlated quantum many-body systems is a very rich problem under heavy investigation. These systems can present many spectacular properties at the macroscopic scale such as superfluidity. Cold atom gases are excellent systems to investigate quantum many-body physics thanks to their great versatility and their high degree of controllability. This thesis deals with the study of the properties of an impurity immersed in a two-component Fermi superfluid, in the BEC-BCS crossover. In this thesis, we measure experimentally the lifetime of boson impurities immersed in a Fermi superfluid, as well as the fermion-impurity interactions. The lifetime measurements not only informs us on the stability of the system but also on the short-range correlations of the Fermi gas by giving us access to the two-body fermionic contact parameter. The study of the impurity-fermion interactions is realized with the analysis of the oscillations of a gas of impurities inside a Fermi superfluid. Finally, we pursue a theoretical study of the phase diagram of an impurity interacting weakly with a Fermi superfluid, as well as a calculation of the polaron energy beyond the mean-field approximation, obtained after a regularization of this 2N+1 body problem using a three-body interaction. Qualitatively speaking, obtaining this energy in the BEC-BCS crossover allows us to bridge between the descriptions of the Bose polaron and the Fermi polaron. Quantitatively-wise, this calculation provides a correction beyond the mean-field term, needed to achieve a percent-level agreement between theory and experiment sought in quantum many-body physics.
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Submitted on : Tuesday, September 28, 2021 - 12:32:10 PM
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  • HAL Id : tel-03356715, version 1

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Matthieu Pierce. Impurity immersed in a two-component Fermi gas. Physics [physics]. Université Paris sciences et lettres, 2019. English. ⟨NNT : 2019PSLEE073⟩. ⟨tel-03356715⟩

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