Light propagation beyond the mean-field theory of standard optics
Prof. Dr. Janne Ruostekoski (Mathematical Sciences, University of Southampton, UK)

The interaction of light with ensembles of resonant emitters is becoming increasingly important for both fundamental research and technological applications as experimentalists realize a growing number of such systems. Comparisons between exact numerical simulations of light propagation in cold and dense atomic ensembles and the predictions obtained from the standard electrodynamics of a polarizable medium (EDPM) reveal that the more than a century-old wisdom of conventional textbook optics can dramatically and qualitatively fail. The failure of EDPM is not due to quantum effects, but reflects emergent cooperative phenomena and strong light-induced correlations between the atoms. However, incorporating the effects of thermal motion in hot atom vapours or inhomogeneous resonance broadening restores the usual phenomenology of effective continuous medium electrodynamics. The strong dipole-dipole interactions also have implications for light propagation in low-loss 1D waveguides filled with atoms that can lead to strongly enhanced atom-light coupling by light confinement, as well as for harnessing the resonant dipole-dipole interactions for preparation of massive subradiant excitations.