Universal optimum quantum cloning and macroscopic quantum state superposition by optical parametric amplification

Summary form only given. The new process of quantum injection into an optical parametric amplifier (OPA) operating in entangled configuration is adopted to "amplify" the quantum entanglement and superposition properties of the photon couples generated by parametric down-conversion. Investigation on the invariance properties of the OPA Interaction Hamiltonian shows that, under certain dynamical conditions, the device may act as a Universal Quantum Cloning Machine (UQCM) of the input qubits. We report the first experimental realization of such a device. The structure of the Wigner function and of the field´s correlation functions show a multiphoton Schroedinger-Cat behaviour of the emitted field which is largely detectable against the squeezed vacuum noise. The realization and a relevant fundamental application of the first "all optical" multiphoton Schrodinger-Cat are reported. The technical and pistemological perspectives of the new methods are considered.