Generation of phase-coherent states

An interaction scheme involving nonlinear chi( 2 )media is suggested for the generationof phase-coherent states (PCSs). The setup is based on parametric amplification of the vacuum followed by up-conversion of the resulting twin beam. The involved nonlinear interactions are studied by the exact numerical diagonalization. An experimentally achievable working regime to approximate PCSs with a high conversion rate is given and the validity of the parametric approximation is discussed.