Usefulness of classical communication for local cloning of entangled states

Rafal Demkowicz-Dobrzanski, Maciej Lewenstein, Aditi Sen De, Ujjwal Sen, Dagmar Bruss

Published 2005-02-16, updated 2006-03-23Version 2

We solve the problem of the optimal cloning of pure entangled two-qubit states with a fixed degree of entanglement using local operations and classical communication. We show, that amazingly, classical communication between the parties can improve the fidelity of local cloning if and only if the initial entanglement is higher than a certain critical value. It is completely useless for weakly entangled states. We also show that bound entangled states with positive partial transpose are not useful as a resource to improve the best local cloning fidelity.