Pauli cloning of a quantum Bit
A family of asymmetric quantum cloning machines is introduced that produce two approximate copies of a single quantum bit, each copy emerging from a Pauli channel. A no-cloning inequality is derived, describing the balance between the quality of the copies. The Pauli cloning machine is also shown to put a limit on the quantum capacity of Pauli channels.
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Ecole Polytechnique, CP 165, Universite Libre de Bruxelles, 1050 Brussels, Belgium and Information and Computing Technologies Research Section, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 and W.