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SUMMARY:Dephrasure channel and superadditivity of coherent information - F
 elix Leditzky (University of Colorado)
DTSTART:20180726T104500Z
DTEND:20180726T113000Z
UID:TALK108394@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:The quantum capacity of a quantum channel captures its capabil
 ity for noiseless quantum communication. It lies at the heart of quantum i
 nformation theory. Unfortunately\, our poor understanding of nonadditivity
  of coherent information makes it hard to understand the quantum capacity 
 of all but very special channels. In this paper\, we consider the dephrasu
 re channel\, which is the concatenation of a dephasing channel and an eras
 ure channel. This very simple channel displays remarkably rich and exotic 
 properties: we find nonadditivity of coherent information at the two-lette
 r level\, a substantial gap between the threshold for zero quantum capacit
 y and zero single-letter coherent information\, a big gap between single-l
 etter coherent and private informations. Its clean form simplifies the eva
 luation of coherent information substantially and\, as such\, we hope that
  the dephrasure channel will provide a much-needed laboratory for the test
 ing of new ideas about nonadditivity.  <br><br><br><br>
LOCATION:Seminar Room 1\, Newton Institute
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