Physics (Internal)

Dicke superradiance and Anderson localization of photons

This event is part of the Biophysics/Condensed Matter Seminar Series.

Abstract: It is generally accepted that coherent multiple scattering of photons in a gas of randomly distributed atoms leads eventually, for a strong enough disorder, to a localized phase where photons are trapped within the gas for extremely long times. The main characteristics of this zero temperature phase transition named after P.W. Anderson are well known and they will be briefly presented. In an atomic gas, however, there exist cooperative effects which change considerably the photon escape rates and the long range atomic dipolar interactions. The resulting enhanced (superradiance) ordecreased (subradiance) emission thus competes with localization effects which are very sensitive to long range correlations between scatterers. The purpose of this talk is to compare the two phenomena and to show that for strong enough disorder, photons become localized but this localization appears as a smooth crossover which is primarily determined by cooperative effects rather than by disorder. This crossover is studied in detail using a universal scaling function whose behavior is obtained both from a microscopic analysis and from a modified stochastic Markov process which shares a lot of similarities with “small world networks” well documented in statistical mechanics.