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--></style><title>MIT Quantum Information Processing Seminar
Announcement</title></head><body>
<div>There will be no MIT QIP Seminar today (Monday March 14); today's
Applied Mathematics Colloquium starting at 16:15 in room 4-231 should
however be a very good substitute:</div>
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<div align="center"><font size="+2"><b>Assisted Capacities of Quantum
Channels</b></font></div>
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<div align="center"><font size="+1"><i>by</i> Charles H. Bennett
(<i>IBM Research, Yorktown Heights</i>)</font></div>
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<div align="center"><u>ABSTRACT</u></div>
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<blockquote>Any process whereby a quantum system passes from a sender
to a receiver, possibly interacting with some environment en
route, may be regarded as a quantum channel. Unlike their
classical analogs, quantum channels have multiple capacities
depending on what one is trying to use them for (e.g. classical
or quantum communication) and what auxiliary resources are brought
into play. I review these capacities and the progress in
associating them with simple entropic expressions such as Holevo
information and quantum mutual information. Among auxiliary
resources, sender-receiver entanglement has a simplifying effect: in
its presence all quantum channels become efficiently
interconvertible (quantum reverse Shannon theorem). By
contrast, classical feedback, or source-independent
bidirectional classical side communication, which have no effect
on a classical channel's single capacity, have a complicated effect on
quantum channels, sometimes increasing both their quantum and
capacities to values between the unassisted and the
entanglement-assisted values. Joint work with Peter Shor, Igor
Devetak, John Smolin and Andreas Winter.</blockquote>
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<div>Next week: MIT Spring Break.</div>
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