  The new process of quantum-injection into an optical parametric amplifier
operating in entangled configuration is adopted to amplify into a large
dimensionality spin 1/2 Hilbert space the quantum entanglement and
superposition properties of the photon-couples generated by parametric
down-conversion. The structure of the Wigner function and of the field's
correlation functions shows a decoherence-free, multiphoton Schroedinger-cat
behaviour of the emitted field which is largely detectable against the
squeezed-vacuum noise. Furthermore, owing to its entanglement character, the
system is found to exhibit multi-particle quantum nonseparability and Bell-type
nonlocality properties. These relevant quantum features are analyzed for
several travelling-wave optical configurations implying different input
quantum-injection schemes
