%0 Journal Article
%J Physical Review Letters
%D 2016
%T Anomalous broadening in driven dissipative Rydberg systems
%A E. A. Goldschmidt
%A T. Boulier
%A R. C. Brown
%A S. B. Koller
%A J. T. Young
%A Alexey V. Gorshkov
%A S. L. Rolston
%A J. V. Porto
%X 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.
%B Physical Review Letters
%V 116
%P 113001
%8 2016/03/16
%G eng
%U http://arxiv.org/abs/1510.08710
%N 11
%R 10.1103/PhysRevLett.116.113001
%0 Journal Article
%J Science
%D 2015
%T 2D Superexchange mediated magnetization dynamics in an optical lattice
%A R. C. Brown
%A R. Wyllie
%A S. B. Koller
%A E. A. Goldschmidt
%A Michael Foss-Feig
%A J. V. Porto
%X The competition of magnetic exchange interactions and tunneling underlies many complex quantum phenomena observed in real materials. We study non-equilibrium magnetization dynamics in an extended 2D system by loading effective spin-1/2 bosons into a spin-dependent optical lattice, and we use the lattice to separately control the resonance conditions for tunneling and superexchange. After preparing a non-equilibrium anti-ferromagnetically ordered state, we observe relaxation dynamics governed by two well-separated rates, which scale with the underlying Hamiltonian parameters associated with superexchange and tunneling. Remarkably, with tunneling off-resonantly suppressed, we are able to observe superexchange dominated dynamics over two orders of magnitude in magnetic coupling strength, despite the presence of vacancies. In this regime, the measured timescales are in agreement with simple theoretical estimates, but the detailed dynamics of this 2D, strongly correlated, and far-from-equilibrium quantum system remain out of reach of current computational techniques.
%B Science
%V 348
%P 540 - 544
%8 2015/04/30
%G eng
%U http://arxiv.org/abs/1411.7036v1
%N 6234
%! Science
%R 10.1126/science.aaa1385