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Guillaume QUESNEL presents


Quantum state and dynamics of coupled Bose-Einstein condensates

and multi-connected Josephson junctions


Thursday 17th of march at 2.00 pm  

Room D420 – Institut Néel

or link:  https://smartvisio.neel.cnrs.fr/b/den-yhi-z0r-axh

Abstract :
Cold atom systems and superconducting junctions are currently two of the main platforms proposed for the realization and quantum simulation of physical models. In this framework, the out-of-equilibrium control of these systems by Floquet-type methods allows to generate and explore a rich class of models. Moreover, where interactions are often negligible in superconducting junctions, they are inherent to cold atomic gases. In this sense, Floquet Engineering of junctions, whether bosonic or superconducting, proves to be an ideal paradigm from the point of view of studying topology, interactions and their coexistence.
In this thesis, I study several quantum systems subjected to periodic forcing.
I present a first study, centered on the Bose-Hubbard model of 2 to 5 sites. In this model the interaction between the atoms is forced periodically and placed in a resonance condition with respect to a given chemical potential configuration. I then show that in these systems it is possible to dynamically generate multi-mode N00N states. The appearance of these states at a given time is explained by a renormalization scheme described by an effective Hamiltonian derived from Floquet theory. In a second step I analyze the effect of chiral microwave radiation, described by a sinusoidal out-of-phase dependence of the potentials, on a metal junction. The analysis by a scattering method allows to confirm the appearance of a chiral current, result already predicted in the framework of a quantum dot junction. In the last part I discuss in more depth the analogy between a Josephson junction and a tight binding model. This representation of a junction as a lattice allows the interpretation of topological transitions when the junction is subjected to microwave radiation. In the context of this analogy I then discuss the notion of edges and the difficulty to realize them in practice. To conclude, I show the effect of an interaction between the quantum dot and the superconductors on the topology of the system.

Thesis Director:

Denis Feinberg