Many-Body Effects in a Frozen Rydberg Gas

We studied the properties of a cold ( ~100μK) and dense ( ~10⁸⁻⁻¹⁰cm^-3) atomic Rydberg Cs gas, and found that the observed widths and shapes of resonances in population transfers cannot be explained in the framework of a usual gas model. We propose a ``frozen Rydberg gas'' model, where the interplay between two-body and many-body phenomena affects in an unexpected way the width and the shape of spectral lines.