Generalized hydrodynamics in strongly interacting 1D Bose gases

Integrable quantum many-body systems, paradigms of exact solvability and mathematical beauty, are now routinely studied in ultracold gases experiments. Control of the effective dimensionality and the degree of isolation in those experiments have given access to the (quasi-)1D regime and the long coherence times necessary to realize (nearly-)integrable systems and to study their quantum dynamics. In integrable systems, the constraints imposed by extensive sets of conserved quantities preclude observables from equilibrating to the traditional thermal expectation values. Instead, observables after equilibration are described by generalized Gibbs ensembles (GGEs). Similarly, the dynamics of such systems over large distances and long times is described by a generalized hydrodynamics (GHD) theory. Central to GHD are the rapidity distributions, which are the momentum distributions of the quasiparticles underlying integrable theories. In this talk, I will show how rapidity distributions can be measured in experiments with 1D gases via a modified time-of-flight procedure. In the Tonks-Girardeau limit, this procedure results in a dynamical fermionization of the bosonic momentum distributions [1,2]. I will then discuss a test of GHD with arrays of 1D bosonic gases [3], as well as our recent exploration of what can happen in such systems before GHD can be applied [4]. Remarkably, we find that after a high-energy quench, energy can be redistributed among distant momentum modes on the fastest available timescale, a process known as hydrodynamization in the context of relativistic heavy-ion collision experiments. Hydrodynamization preceeds local prethermalization, and we conjecture that GHD can be applied right after hydrodynamization [4].