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SUMMARY:Entropy of a correlation matrix and (in)fidelity between several q
 uantum states - Karol Zyczkowski (Jagiellonian University Cracow\, Poland)
DTSTART:20110127T141500Z
DTEND:20110127T151500Z
UID:TALK28506@talks.cam.ac.uk
CONTACT:Ashley Montanaro
DESCRIPTION:Making use of the strong subadditivity of entropy we prove tha
 t the Holevo quantity for an ensemble of k quantum states is not larger th
 an the entropy of a certain correlation matrix. In the case of k=2 states\
 nthe minimum over the set of admissible correlation matrices is found to b
 e given by a function of the fidelity between both states. This implies an
  upper bound for the coherent information and the quantum\nJensen--Shannon
  divergence. Restricting our attention to classical information we bound t
 he transmission  distance between any two probability distributions by the
  entropic distance\, which is a concave function of the Hellinger distance
 .\n\nFor larger number of k states in an ensemble we find\nexplicit bounds
  for the exchange entropy\, which could  be used to characterize distingui
 shability between them.
LOCATION:MR13\, Centre for Mathematical Sciences
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