TY - JOUR T1 - Anomalous broadening in driven dissipative Rydberg systems JF - Physical Review Letters Y1 - 2016 A1 - E. A. Goldschmidt A1 - T. Boulier A1 - R. C. Brown A1 - S. B. Koller A1 - J. T. Young A1 - Alexey V. Gorshkov A1 - S. L. Rolston A1 - J. V. Porto AB - We observe interaction-induced broadening of the two-photon 5s-18s transition in 87Rb atoms trapped in a 3D optical lattice. The measured linewidth increases by nearly two orders of magnitude with increasing atomic density and excitation strength, with corresponding suppression of resonant scattering and enhancement of off-resonant scattering. We attribute the increased linewidth to resonant dipole-dipole interactions of 18s atoms with spontaneously created populations of nearby np states. Over a range of initial atomic densities and excitation strengths, the transition width is described by a single function of the steady-state density of Rydberg atoms, and the observed resonant excitation rate corresponds to that of a two-level system with the measured, rather than natural, linewidth. The broadening mechanism observed here is likely to have negative implications for many proposals with coherently interacting Rydberg atoms. VL - 116 U4 - 113001 UR - http://arxiv.org/abs/1510.08710 CP - 11 U5 - 10.1103/PhysRevLett.116.113001 ER -