Improving the fidelity of quantum cloning by field-induced inhibition of the unwanted transition

Abstract

The fidelity of quantum cloning is very often limited by the accompanying unwanted transitions. We show how the fidelity can be improved by using a coherent cycling field to inhibit the unwanted transitions. We demonstrate this explicitly in the context of the model of Simon et al. [J. Mod. Opt. 47, 233 (2000); Phys. Rev. Lett. 84, 2993 (2000)]. We also investigate the effects of the number of atoms on the quality of quantum cloning. We show the state dependence of the scheme, however all the input states of the qubit can be cloned equally well by choosing the cycling field accordingly.