Thermalization of a system of nearly harmonic ladders*

The study of the dynamics of ultracold Rydberg atoms in a magneto-optical trap offers insight into the thermalization of closed, isolated quantum systems. We excite the atoms to the middle of the n∽34 manifold in a small electric field. These Stark levels form a nearly harmonic ladder so that energy spreads out from the center of the manifold via dipole-dipole interactions among the atoms. We use the notion of dynamical typicality to numerically predict the thermalized state and compare this to the observed equilibrium energy distribution at various Rydberg atom densities. Our results reveal that, especially at low densities, our system fails to thermalize.