Quantum Superposition of Parametrically Amplified Multiphoton Pure States Whitin a Decoherence-free Schroedinger-cat Structure

The new process of quantum-injection into an optical parametric amplifier operating in entangled configuration is adopted to amplify into a large dimensionality spin-12 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 multiparticle quantum nonseparability and Bell-type nonlocality properties. These relevant quantum features are analyzed for several travellingwave optical configurations implying different input quantum-injection schemes. (PACS numbers: 03.65.Bz, 03.67.-a, 42.50.-p, 89.70.+c).