Assisted cloning of an arbitrary unknown two-qubit state via a genuine four-qubit entangled state and positive operator-valued measure

Abstract

A protocol for cloning an arbitrary unknown two-qubit state and its orthogonal complement state with the assistance of a state preparer is presented. In this paper, a genuine four-particle entangled state which cannot be reduced to the product of two Bell states is used as the quantum channel. Moreover, positive operator-valued measure (POVM) instead of usual projective measurement is employed. In one hand, the usual teleportation is required. And in another hand, the perfect copies and complement copies of an unknown two-particle state can be implemented with a certain probability in the help of the state preparer.