Generation of phase-coherent states
  An interaction scheme involving nonlinear $\chi^{(2)}$ media is suggested for the generation of phase-coherent states (PCS). The setup is based on parametric amplification of 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 PCS with high conversion rate is given, and the validity of parametric approximation is discussed. 
Giacomo M. D'Ariano, Matteo G. A. Paris and Massimiliano F. Sacchi   (Quantum Optics Group -- University of Pavia)