Realization of the Dicke model using cavity-assisted Raman transitions
  We realize an open version of the Dicke model by coupling two hyperfine ground states using two cavity-assisted Raman transitions. The interaction due to only one of the couplings is described by the Tavis-Cummings model and we observe a normal mode splitting in the transmission around the dispersively shifted cavity. With both couplings present the dynamics are described by the Dicke model and we measure the onset of superradiant scattering into the cavity above a critical coupling strength. 
Markus P. Baden, Kyle J. Arnold, Arne L. Grimsmo, Scott Parkins and   Murray D. Barrett
quant-ph physics.atom-ph