Additivity for unital qubit channels

@article{King2001AdditivityFU,
  title={Additivity for unital qubit channels},
  author={Christopher King},
  journal={Journal of Mathematical Physics},
  year={2001},
  volume={43},
  pages={4641-4653}
}
  • C. King
  • Published 28 March 2001
  • Mathematics, Physics
  • Journal of Mathematical Physics
Additivity of the Holevo capacity is proved for product channels, under the condition that one of the channels is a unital qubit channel, with the other completely arbitrary. As a byproduct this proves that the Holevo bound is the classical information capacity of such qubit channels, and provides an explicit formula for this classical capacity. Additivity of minimal entropy and multiplicativity of p-norms are also proved under the same assumptions. The proof relies on a new bound for the p… 
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An upper bound for the minimum output entropy of a unital quantum channel is found, and an exact formula for general qubit channels is obtained that gives the precise quantity of classical capacity of the Werner–Holevo channel.
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