Fig. 6.

Polyatomic Rb molecules and many-body spectra. a The observation of polyatomic s-wave Rydberg molecules (dimers, trimers, and tetramers) in photoassociation of Rydberg molecules; figure reprinted from ref. ⁷³, b density averaged absorption spectra for Rb(71s) excitations. In a, the gas is thermal at T = 0.5 μK and the MOT center density is ρ = 1.7 × 10¹² cm⁻³. The laser profile illuminates the cloud over the full cylindrical radius (black) and in a small waist (dashed, blue); data is reported in Gaj et al.⁷³. In b, the density averaged absorption spectrum at T/T_c = 0.47 for a partially condensed gas of (zero temperature) at peak density ρ = 2.3 × 10¹⁴ cm⁻³. Reprinted figure with permission from ref. ⁷⁷ Copyright (2016) by the American Physical Society