Quantum-state cloning in the presence of a closed timelike curve

Using the Deutsch model of closed timelike curves, we show that a universal cloner can be constructed that when acting on a completely arbitrary qubit state, exceeds the no-cloning bound for fidelity. Since the no-cloning theorem has played a central role in the development of quantum information science, it is clear that the existence of closed timelike curves that behave according to Deutsch's model would radically change the rules for quantum information technology. Nevertheless, we show that this type of cloning does not violate no-signaling criteria.