[Séminaire atomes froids] Nicolas Cherroret (LKB)

Non-thermal fixed points in far-from-equilibrium 3D Bose gases

Résumé: 

Following a quantum quench, local observables in many-body systems typically thermal-
ize. In certain cases, however, this thermalization occurs via a two-stage process: the system
first exhibits universal dynamical scaling laws with strongly non-thermal properties, before
eventually reaching thermal equilibrium on a longer time scale. This phenomenon is referred
to as a non-thermal fixed point.
In this talk, I will discuss the non-thermal fixed point that emerges when a 3D Bose gas is
quenched across the condensation transition. I will show that it generally involves a transient
"weak turbulence" regime, followed at later times by a coarsening dynamics associated with
the slow recombination of vortex lines. Quenches performed exactly at the critical point, in
contrast, display a distinct coarsening dynamics, presumably without vortices but involving
the diffusion of critical fluctuations. If time permits, I will also discuss the robustness of
this universal dynamics against external perturbations, typically disorder and drive.