Relaxation of an Isolated Dipolar-Interacting Rydberg Quantum Spin System

How do isolated quantum systems approach an equilibrium state? We experimentally and theoretically address this question for a prototypical spin system formed by ultracold atoms prepared in two Rydberg states with different orbital angular momenta. By coupling these states with a resonant microwave driving, we realize a dipolar XYspin-1/2model in an external field. Starting from a spin-polarized state, we suddenly switch on the external...