Optomechanical Cavity Cooling of an Atomic Ensemble

We demonstrate cavity sideband cooling of a single collective motional mode of an atomic ensemble down to a mean phonon occupation number ⟨n⟩min⁡=2.0[subscript -0.3][superscript +0.9]. Both ⟨n⟩[subscript min]⁡ and the observed cooling rate are in good agreement with an optomechanical model. The cooling rate constant is proportional to the total photon scattering rate by the ensemble, demonstrating the cooperative character of the light-emission-induced cooling process. We deduce fundamental limits to cavity cooling either the collective mode or, sympathetically, the single-atom degrees of freedom.National Science Foundation (U.S.)United States. Defense Advanced Research Projects AgencyMIT-Harvard Center for Ultracold AtomsHertz FoundationNatural Sciences and Engineering Research Council of Canada (NSERC)National Science Foundation (U.S.) Integrative Graduate Education and Research Traineeship Progra