  Generic far-away-from-equilibrium many-body dynamics involve entropy
production, and hence are thermodynamically irreversible. Near quantum critical
points, an emergent conformal symmetry can impose strong constraints on entropy
production rates, and in some cases completely forbid entropy production, which
usually occurs for systems that deviate from quantum critical points. In this
article, we illustrate how the vanishing entropy production near a quantum
critical point results in reversible far-away-from-equilibrium dynamics at
finite temperatures that are otherwise irreversible. Away from the quantum
critical point, the quantum dynamics are damped, and our analysis directly
relates the thermalization time scale to the hydrodynamic viscosity near
quantum critical points with dynamical critical exponent $z=2$. We demonstrate
how both controllable reversible and irreversible dynamics can be potentially
studied in cold gas experiments using Feshbach resonances.

Quantum Gases