Generalized universal cloning and purification in quantum information by multistep state symmetrization

A general multistep linear state symmetrization device for photonic qubits is presented together with the experimental realizations of the 1 -> 3 and 2 -> 3 universal optimal quantum cloning machines and of a 3-qubit purification procedure. Since the present method exploits the bosonic nature of the photons, it can be applied to any particle obeying to the Bose statistics. On a technological perspective, the present protocol is expected to find relevant applications as a multiqubit symmetrization device to be used in modern quantum-information networks.