Bruß, Dagmar and DiVincenzo, David P. and Ekert, Artur and Fuchs, Christopher A. and Macchiavello, Chiara and Smolin, John A. (1998) Optimal universal and state-dependent quantum cloning. Physical Review A, 57 (4). pp. 2368-2378. ISSN 1050-2947 http://resolver.caltech.edu/CaltechAUTHORS:BRUpra98
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We establish the best possible approximation to a perfect quantum cloning machine that produces two clones out of a single input. We analyze both universal and state-dependent cloners. The maximal fidelity of cloning is shown to be 5/6 for universal cloners. It can be achieved either by a special unitary evolution or by a teleportation scheme. We construct the optimal state-dependent cloners operating on any prescribed two nonorthogonal states and discuss their fidelities and the use of auxiliary physical resources in the process of cloning. The optimal universal cloners permit us to derive an upper bound on the quantum capacity of the depolarizing quantum channel.
|Additional Information:||©1998 The American Physical Society Received 23 May 1997; revised 11 November 1997 We thank Vladimir Bužek and Nicolas Gisin for discussions. This work was supported in part by European TMR Research Network Grant No. ERB-4061PL95-1412 and a NATO collaborative research grant. D.P.V. and J.A.S. thank the Army Research Office for support. C.A.F. would like to thank the Lee A. DuBridge Foundation for financial support. He also acknowledges support from DARPA through the Quantum Information and Computing Institute administered by the U.S. Army Research Office. Part of this work was completed during the Elsag-Bailey–ISI Foundation research meeting on quantum computation.|
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