Assisted Cloning and Orthogonal Complementing of an Arbitrary Two-qubit State

We propose a scheme to create a perfect copy or a complement copy of an arbitrary bipartite state with assistance from a state preparer. The scheme contains a two-qubit state teleportation from a sender to a receiver by using two partially entangled pairs as quantum channel. After the teleportation, to help the sender to clone the initial state, the state preparer performs an appropriate bipartite projective measurement and informs the sender of the measurement result. It is found that the exact copying and complementing of the arbitrary two-qubit state can be produced probabilistically with unity fidelity, and the success probability of perfect cloning will peak to 1 if the original state is chosen from some special ensembles.