Superbroadcasting of mixed states

Abstract

We derive the optimal universal broadcasting for mixed states of qubits. We show that the nobroadcasting theorem cannot be generalized to more than a single input copy. Moreover, for four or more input copies it is even possible to purify the input states while broadcasting. We name such purifying broadcasting superbroadcasting.

4 pages, 4 figures, to appear on Phys. Rev. Lett