Generation of non-classical optical fields by a beam splitter with   second-order nonlinearity
  We propose quantum-mechanical model of a beam splitter with second-order nonlinearity and show that non-classical features such as squeezing and sub-Poissonian photon statistics of optical fields can be generated in output fundamental and second harmonic modes when we mix coherent light beams via such a nonlinear beam splitter. 
Hari Prakash and Devendra Kumar Mishra
quant-ph physics.optics