On Shor ’ s channel extension and constrained channels

نویسندگان

  • A. S. Holevo
  • M. E. Shirokov
چکیده

Several equivalent formulations of the additivity conjecture for constrained channels, which formally is substantially stronger than the unconstrained additivity, are given. To this end a characteristic property of the optimal ensemble for such a channel is derived, generalizing the maximal distance property. It is shown that the additivity conjecture for constrained channels holds true for certain nontrivial classes of channels. After giving an algebraic formulation for the Shor's channel extension, its main asymptotic property is proved. It is then used to show that additivity for two constrained channels can be reduced to the same problem for unconstrained channels, and hence, " global " additivity for channels with arbitrary constraints is equivalent to ad-ditivity without constraints.

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تاریخ انتشار 2004