Séminaires du jeudi 08 juin

Séminaire du LPTMS: Duncan O'Dell *** séminaire exceptionnel ***


Quantum catastrophes

Duncan O’Dell (McMaster University)

Catastrophe theory provides a unified description of a broad range of singularities and defects in fields and has been applied extensively in optics. A key idea is that of scale: at large scales the catastrophe appears singular but at smaller scales it is smoothed, e.g. by wave interference. In 2004 Michael Berry and Mark Dennis suggested that waves might themselves display singularities which are only smoothed by the fundamental discreteness of quantum field excitations (e.g. photons). In this talk I will give examples of such “quantum catastrophes” appearing in the dynamics of simple quantum systems such as a Josephson junction made from two BECs following a quench.  I will emphasize that, owing to the structural stability of catastrophes and their scaling properties, quantum catastrophes represent a universal aspect of quantum dynamics.

Séminaire FAST-LPTMS: Mark Hoefer


The hydraulic analogy to superfluid-like dispersive hydrodynamics

Mark Hoefer (Department of Applied Mathematics, University of Colorado,  Boulder, USA)

The classic "hydraulic analogy" between supercritical shallow water flows and gas dynamics was leveraged in the early to mid 20th century as a means to model the flow patterns around wings with a relatively simple water table. But this analogy breaks down when water wave dispersion is strong relative to dissipative effects as in oscillatory, undular bores. In this regime, the more appropriate analogy is to dispersive hydrodynamic media such as superfluids and nonlinear optical diffractive or dispersive patterns, where dispersive shock waves (DSWs), also called quantum and optical shock waves, have been observed. In this talk, the problem of steady pattern formation in supercritical, shallow water flows will be examined theoretically and experimentally. Two new, non-classical types of oscillatory DSWs will be identified within the context of the fifth order Kawahara equation resulting from a balance between capillarity and gravity at water depths on the order of 0.5 cm. Experiments with a shallow water table demonstrate their physical existence and properties. The results presented have implications for dispersive hydrodynamic media with non-convex linear dispersion curvature such as ultracold atomic superfluids and nonlinear fiber optics. Voir l'annonce du FAST: https://semmeca.limsi.fr/affiche/res17_15.html

************************* ATTENTION **************************** l'exposé est donné au FAST : accès, cf. http://www.fast.u-psud.fr/fr/plan ******************************************************************