Approximate quantum cloning and the impossibility of superluminal information transfer - art. no. 062302

We show that nonlocality of quantum mechanics cannot lead to superluminal t ransmission of information, even if most general local operations are allow ed, as long as they are linear and trace preserving. In particular, any qua ntum-mechanical approximate cloning transformation does not allow signaling . On the other hand, the no-signaling constraint on its own is not sufficie nt to prevent a transformation from surpassing the known cloning bounds. We illustrate these concepts on the basis of some examples.