Quantum noise and correlations in resonantly enhanced wave mixing based   on atomic coherence
  We investigate the quantum properties of fields generated by resonantly enhanced wave mixing based on atomic coherence in Raman systems. We show that such a process can be used for generation of pairs of Stokes and anti-Stokes fields with nearly perfect quantum correlations, yielding almost complete (i.e. 100%) squeezing without the use of a cavity.   We discuss the extension of the wave mixing interactions into the domain of a few interacting light quanta. 
M.D.Lukin, A.B.Matsko, M. Fleischhauer, and M.O.Scully