Rydberg excitations interacting with helium droplets

We develop a self-consistent theoretical description of Rydberg atoms interacting with superfluid helium droplets, where the ionic core is solvated by helium. The resulting electronic spectrum separates into two distinct classes of droplet-dressed Rydberg states, corresponding to electronic probability density localized close to or far from the solvated ionic core. The inner droplet-dressed states are strongly influenced by the droplet density and can serve as sensitive probes of droplet structure and dielectric response. For the outer droplet-dressed states, the radial force generated by the finite polarizable droplet lifts the angular momentum degeneracy of the Rydberg manifold in a non-perturbative fashion, producing spectral signatures that scale with droplet size and density. Remarkably, a subset of these states remains quasi-degenerate, enabling binding of the Rydberg electron to neutral alkali atoms via a trilobite-like mechanism and giving rise to molecular states with exceptionally large dipole moments.