Soutenance de thèse: Mathieu Isoard

Theoretical study of quantum correlations and nonlinear fluctuations in quantum gases


Mathieu Isoard



Matteo Conforti, Université Lille, rapporteur

Patrik Öhberg, Heriot-Watt University, rapporteur

Élisabeth Giacobino, CNRS, examinatrice

Sandro Stringari, University of Trento, examinateur

Chris Westbrook, Institut d’Optique, examinateur

Nicolas Pavloff, Université Paris-Saclay/CNRS , directeur de thèse



This thesis is dedicated to the study of nonlinear-driven phenomena in two quantum gases which bear important similarities: Bose-Einstein condensates of ultracold atomic vapors and paraxial nonlinear laser beam.

These systems can be described within a hydrodynamic framework which make it possible to investigate their short and long time propagation by means of mathematical methods developed by Riemann and Whitham. In particular, we study the formation and the propagation of dispersive shock waves which arise after a wave breaking event. We obtain a kind of a weak shock theory, from which we can extract a quantitative description of experimentally relevant parameters, such as the velocity of the solitonic edge of the shock or the contrast of its fringes.

In a second part, we study sonic analogues of black holes. In a Bose-Einstein condensate, it is possible to implement a stationary configuration with a current flowing from a subsonic region to a supersonic one. This mimics a black hole, since sonic excitations cannot escape the supersonic region. Besides, quantizing the phonon field leads to a sonic analogue of Hawking radiation. In this thesis, we have shown that a correct account of zero modes is essential for an accurate description of the Hawking process, and results in a excellent comparison with recent experimental datas. In addition, we characterize the entanglement shared among quantum excitations and show that they exhibit tripartite entanglement.

Date/Time : 10/09/2020 - 14:00 - 16:30

Location : Grand amphi, bâtiment Pascal n° 530

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