Abstract: It is notoriously hard to calculate the out-of-equilibrium
dynamics of many-body quantum systems. While confining particles to
one dimension sometimes simplifies dynamics, even in 1D, dynamical
solutions have usually been elusive. A new approximate theory,
generalized hydrodynamics (GHD), can model previously intractable
dynamics. But are GHD’s approximations valid? I will describe a series
of experiments with 1D Bose gases taken very far from equilibrium by,
for instance, making sudden trap changes that lead them to compress
35-fold. We study the evolving distribution of rapidities, which are the
momenta of the quasiparticles that emerge in these many-body systems,
and which we only recently first experimentally observed for equilibrium
1D gases. These out-of-equilibrium experiments allow us to test the
underlying assumptions of GHD across coupling regimes. As I will show,
we find excellent agreement between our experiments and GHD theory.