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Using local additivity to find examples of superadditivity of quantum channels

Presented by: 
Beth Ruskai
Thursday 26th July 2018 - 16:45 to 17:30
INI Seminar Room 1
The local additivity of minimal output entropy can be extended to local additivity of maximal relative entropy with respect to a fixed reference state. This can be exploited to test channels for superadditivity of Holevo capacity with numerical effort comparable to searching for the minimal output entropy. Local maxima which do not arise from product inputs play a key role.  Moreover, evidence of superadditivity can be found even if the additivity violation itself is too small to be seen numerically.  A  max-min expression for the capacity, dues to Petz, et al, plays a key role.

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University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons