State-Dependent Energy Shifts of Rydberg Atoms in a Ponderomotive Optical Lattice

We demonstrate the state dependence of the ponderomotive energy shift of Rydberg atoms in an optical lattice using microwave spectroscopy. Unique to Rydberg atoms, this dependence results from a state-dependent aspect ratio between Rydberg-atom size and lattice period. A semiclassical simulation reproduces all features observed in the microwave spectra and indicates the presence of trapped Rydberg atoms.