Observation of quasi-ballistic transport at infinite temperature in a Rydberg simulator

Conventional belief dictates a dichotomy in interacting quantum dynamics: (i) in fine-tuned models, one observes nontrivial, long-lived dynamical phenomena, (ii) without fine-tuning, the dynamics is described by relaxation to thermal equilibrium according to hydrodynamic equations. In this work, we make two unexpected observations in the non-equilibrium dynamics of a Rydberg quantum simulator. We observe the ballistic propagation of correlations over large distances at infinite temperature, as well as long-lived static correlations above a thermal background. While the latter observation can be explained by new sets of scar states, our theoretical analysis reveals the former originates from unconventional transport mechanisms associated with the constrained Hilbert space due to the Rydberg blockade. This gives rise to a long-lived quasiparticle with a well-defined band structure at infinite temperature. Our analysis yields further predictions, including a crossover between diffusive and ballistic universality classes at intermediate lengthscales, and sheds light on the interplay between hydrodynamic transport and operator spreading. Finally, our study of the long-lived correlations brings new insight into the physics of many-body scars in Rydberg atom arrays, finding new families of scars as well as observables which prominently show scar physics, yet also differentiate between these families. Taken together, our results reveal new surprises from a simple quantum quench experiment, highlighting that much remains unexplored in the field.