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Dynamics and stability of a Bose-Fermi mixture : counterflow of superfluids and inelastic decay in a strongly interacting gas

Abstract : Understanding the effect of interactions in quantum many-body systems presents some of the most compelling challenges in modern physics. Ultracold atoms have emerged as a versatile platform to engineer and investigate these strongly correlated systems. In this thesis, we study the properties of a mixture of Bose and Fermi superfluids with tunable interactions produced using ultracold vapors of ⁷Li and ⁶Li. We first study the hydrodynamic properties of the mixture by creating a counterflow between the superfluids. The relative motion only exhibit dissipation above a critical velocity that we measure in the BEC-BCS crossover. A numerical simulation of counterflowing condensates allows for a better understanding of the underlying mechanisms at play in the dynamics. In particular, this numerical study provides additional evidence that the onset of friction in our experiment is due to the simultaneous generation of elementary excitations in both superfluids. Finally, we consider the inelastic losses that occur via three-body recombination in our cold gases. This few-body process is intimately related to short-distance correlations and is thereby connected to the universal properties of the many-body system. This manifests as the apparition of an unusual dependence on density or temperature in the loss rate when increasing the interactions. We demonstrate this effect in two examples where interactions are resonant: the case of a dilute unitary Bose gas and the one of impurities weakly coupled to a unitary Fermi gas. More generally, our work shows that inelastic losses can be used to probe quantum correlations in a many-body system.
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Submitted on : Friday, June 1, 2018 - 2:40:07 PM
Last modification on : Wednesday, October 14, 2020 - 3:49:21 AM
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  • HAL Id : tel-01805141, version 1


Sébastien Laurent. Dynamics and stability of a Bose-Fermi mixture : counterflow of superfluids and inelastic decay in a strongly interacting gas. Quantum Gases [cond-mat.quant-gas]. Université Paris sciences et lettres, 2017. English. ⟨NNT : 2017PSLEE023⟩. ⟨tel-01805141⟩



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