Schroedinger cat states and optimum universal quantum cloning by entangled parametric amplification

The new process of quantum-injection by a single-photon in a pure quantum superposition state into an optical parametric amplifier operating in entangled configuration is adopted to generate an all optical multiphoton Schroedinger-cat state which is largely detectable against the squeezed-vacuum noise. 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 based on stimulated emission process in an optical parametric amplifier. (C) 2000 Elsevier Science B.V. All rights reserved.