  The Dicke model consisting of an ensemble of two-state atoms interacting with
a single quantized mode of the electromagnetic field exhibits a
zero-temperature phase transition at a critical value of the dipole coupling
strength. We propose a scheme based on multilevel atoms and cavity-mediated
Raman transitions to realise an effective Dicke system operating in the phase
transition regime. Output light from the cavity carries signatures of the
critical behavior which is analyzed for the thermodynamic limit where the
number of atoms is very large.
