Assisted cloning of an unknown two-particle entangled state

We propose a protocol where one can realize quantum cloning of an unknown two-particle entangled state and its orthogonal complement state with assistance offered by a state preparer. The first stage of the protocol requires usual teleportation via two entangled particle pairs as quantum channel. In the second stage of the protocol, with the assistance (through a two-particle projective measurement) of the preparer, the perfect copies and complement copies of an unknown state can be produced. We also put forward a scheme for the teleportation by using non-maximally entangled quantum channel. The clones and complement clones of unknown state can be obtained with certain probability in the latter scheme. (C) 2005 Elsevier B.V. All rights reserved.