Hydrodynamic Attractor in Periodically Driven Ultracold Quantum Gases

Hydrodynamic attractors characterize hydrodynamiclike evolution in strongly interacting systems, independent of initial conditions or microscopic details, outside the conventional hydrodynamic regime. They explain why hydrodynamic models apply to high-energy nuclear collisions, but so far have only been explored for monotonic expansion, such as Bjorken flow. We demonstrate that a system undergoing periodic expansion and contraction exhibits a novel cyclic attractor behavior. We employ Müller-Israel-Stewart theory to a driven ultracold Fermi gas to predict the shape of the attractor, which does not converge to Navier-Stokes dynamics at late times. This phenomenon can be measured in real time in ultracold quantum gases with externally modulated scattering length, offering a new avenue for the experimental discovery of hydrodynamic attractors.