Quantum Gas Microscopy of Ground-State Phases in the Fermi?Hubbard Model
Monday, 28 September 2026
16:30
SFB1225 ISOQUANT
YRC DInner Seminar: Clemens Werthmann
Lessons on the general form of hydrodynamic attractors from cold atoms and classical Yang-Mills theory
Institut für Theoretische Physik, PI, Goldene Box
In certain systems, complex far-from-equilibrium dynamics in a wide range of time evolution trajectories quickly lose memory of their initial conditions and make way to universal phenomena that simplify the system's state. A prominent example is the hydrodynamic attractor, which appears in the Bjorken flow model of early time dynamics in heavy ion collisions. The fact that the presence of an attractor significantly reduces the complexity of the system's dynamics can be used to derive prediction formulae for the evolution of the system, and even to construct effective dynamical descriptions. The conformal Bjorken flow attractor is, however, a particularly simple example case. Concepts and characterizations that were derived in this case may not carry over to the general phenomenology of an attractor. In this talk, I will first briefly review what is known about the hydrodynamic attractor in Bjorken flow and then discuss how expectations from this simple case are broken in two newly discovered examples of attractors. The attractor in ultracold atomic gases is a promising avenue for a direct experimental detection of attractor behaviour. It is in many ways distinct from the heavy ion case, proving that the phenomenon extends to many more systems than the original formulation may indicate. However, in strongly driven systems heating will obscure a collapse onto a universal curve in single observables. The behaviour must instead be diagnosed via a method that considers dimensional reduction in the full state space. The earliest times of heavy ion collision features high gluon occupations, which may be described as classical fields. This motivates a study of hydrodynamic attractor behaviour in classical Yang-Mills theory with Bjorken-like symmetries. A major difference to other dynamical descriptions in which the behaviour has been diagnosed is the fact that this theory does not hydrodynamize. Indeed, it features only expansion driven, but no interaction driven memory loss. Even more strikingly, some of the lost memory is recovered again while expansion still dominates the dynamics. These new features break with the traditional picture of the attractor and must be considered in future models that aim to formulate a generalized effective description of universal dynamics.
