Energy transport in a system of nearly harmonic ladders*

We excite a sample of ultracold atoms to Rydberg states in the presence of a static electric field. By choosing a state in the middle of the Stark manifold we form a system of nearly harmonic ladders that can exchange energy via dipole-dipole interactions. We measure the density dependence of population redistribution among the manifold states using microwave spectroscopy. We have also developed a computational model that includes about 50 manifold energy levels. Our simulation results compare favorably to the experimental data and suggest that three-body interactions may play an important role.