Characterization of low-cost one-to-two qubit cloning
Thomas Durt, Jiangfeng Du · Physical Review A · 2004
In this paper we establish a deep connection between the 3-qubit one-to-two phase-covariant quantum cloning network of Fuchs et al. [Phys. Rev. A 56, 1163 (1997)], and its low-cost two-qubit counterpart due to Niu and Griffiths [Phys. Rev. A 60, 2764 (1999)]. A general, necessary, and sufficient criterion is derived in order to characterize the reducibility of 3-qubit one-to-two cloners to two-qubit one-to-two cloners. When this criterion is fulfilled, low-cost cloning is possible. We show that the optimal isotropic or universal 3-qubit one-to-two cloning machine is not reducible to a 2-qubit one-to-two cloner.