Out-of-equilibrium 1D Bose gases and generalized hydrodynamics

The theory of generalized hydrodynamics (GHD) takes advantage of nearly perfect conservation laws in nearly integrable systems to accomplish the otherwise difficult task of predicting their dynamical behavior. We will describe experiments with quenched 1D Bose gases that validate GHD. We will then show how certain sudden quenches can temporarily invalidate the assumptions that underly GHD. For very short times "hydrodynamization" occurs, during which energy rapidly redistributes among different modes and GHD does not work. At somewhat longer times "local prethermalization" occurs, during which GHD can still work quite well although the nominal GHD assumptions do not hold. Finally, we will illustrate, with new experimental and theoretical evidence, the conditions needed for there to be distinct hydrodynamization and local prethermalization time scales. We suspect that these considerations qualitatively hold for energetic quenches in all many-body quantum systems, integrable or not.