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