Universal quantum cloning and macroscopic superposition in parametric amplification

The new process of quantum-injection into an optical parametric amplifier operating in entangled configuration is adopted to amplify into a large dimensionality spin1/2 Hilbert space the quantum entanglement and superposition properties of the photon-couples generated by parametric down-conversion. The invariance properties of the OPA interaction hamiltonian show that, under certain conditions, the device may act as a Universal Quantum Cloning Machine (UQCM) of the input qubits. Preliminary results here reported show the first experimental realization of such a device. The structure of the Wigner function and of the field's correlation functions shows a multiphoton Schrödinger-cat behaviour of the emitted field which is largely detectable against the squeezed-vacuum noise.