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Theses

Gaz quantique dans un potentiel périodique dépendant du temps : de la modulation perturbative aux résonances de l'effet tunnel assisté par le chaos

Maxime Arnal 1, 2
2 Atomes Froids (LCAR)
LCAR - Laboratoire Collisions Agrégats Réactivité
Abstract : Degenerate quantum gases have demonstrated their ability to mimic the properties of other systems and are, as such, an ideal platform for quantum simulation. These gases, characterized by a high level of control thanks to the temporal driving of their parameters, have mainly been studied either in the perturbative regime or in a purely chaotic one. The aim of the present work is to further extend the possibilities offered by such systems by taking advantage of a mixed dynamics, which we apply to the case of matter-wave transport. In this thesis, we describe several experimental studies on the dynamics of a Bose-Einstein condensate in a one-dimensional time-dependent optical lattice. The experiments that are presented fall into two categories: (i) the perturbative regime, where the applied modulations induce little chaos, and (ii) the mixed regime, where regular and chaotic trajectories coexist at the classical limit. In the perturbative regime, which was first studied during this thesis, we distinguish two modulation domains of the optical lattice. When the modulation frequencies are resonant with the band structure, we induce interband transitions that are subject to selection rules. We then demonstrate a new cooling technique, similar to evaporation but in reciprocal space, taking advantage of these selection rules. For a phase modulation out of resonance, the dynamics of the condensate can be described by an effective Hamiltonian. We study two such Hamiltonians, one of which accounts for a quantum phase transition and the other for the renormalization of the lattice depth. In each case we explore the limits of these models. The mixed regime constitutes the second focus of this thesis. The classical analogue of our system is the modulated pendulum, well-known to present both regular and chaotic trajectories. This behavior is revealed at the quantum level by the presence, in addition to the lattice structure, of a chaotic sea. In this optical lattice dressed by chaos, we study a type of transport called chaos-assisted tunneling, which presents resonances that can amplify or inhibit tunneling between two stable positions within a lattice well. Compared to previous experiments on this subject, we use a different configuration in which we manage to resolve these resonances for the first time. For quantum simulators, this work paves the way to a new type of control, including long-range transport.
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https://tel.archives-ouvertes.fr/tel-02976831
Contributor : Maxime Arnal <>
Submitted on : Friday, October 23, 2020 - 4:30:44 PM
Last modification on : Monday, November 23, 2020 - 9:55:10 AM

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  • HAL Id : tel-02976831, version 1

Citation

Maxime Arnal. Gaz quantique dans un potentiel périodique dépendant du temps : de la modulation perturbative aux résonances de l'effet tunnel assisté par le chaos. Gaz Quantiques [cond-mat.quant-gas]. Université Toulouse 3 Paul Sabatier, 2020. Français. ⟨tel-02976831⟩

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