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
@article{arxiv.quant-ph/9905048,
title = {Quantum Superposition of Parametrically Amplified Multiphoton Pure States whitin a Decoherence-Free Schroedinger-Cat Structure},
author = {F. A. Bovino and F. De Martini and V. Mussi},
journal= {arXiv preprint arXiv:quant-ph/9905048},
year = {2007}
}