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SUMMARY:Entanglement-assisted communication of classical and quantum infor
 mation -  Min-Hsiu Hsieh
DTSTART:20100204T141500Z
DTEND:20100204T151500Z
UID:TALK22996@talks.cam.ac.uk
CONTACT:Jonathan
DESCRIPTION:We consider the problem of transmitting classical and quantum 
 information reliably over an entanglement-assisted quantum channel (EACQ c
 oding). Our main result is a capacity theorem that gives a three-dimension
 al region containing all achievable rates. Points in the capacity region a
 re rate triples\, consisting of the classical communication rate\, the qua
 ntum communication rate\, and the entanglement consumption rate of a parti
 cular coding scheme. The crucial protocol in achieving the boundary points
  of the capacity region is a protocol that we name the classically-enhance
 d father protocol. The classically-enhanced father protocol is more genera
 l than any other protocol in the family tree of quantum Shannon theoretic 
 protocols\, in the sense that several previously known quantum protocols a
 re now child protocols of it. The classically-enhanced father protocol als
 o shows an improvement over a time-sharing strategy for the case of a qubi
 t dephasing channel—this result justifies the need for simultaneous codi
 ng of classical and quantum information over an entanglement-assisted quan
 tum channel. Our capacity theorem is of a multi-letter nature (requiring a
  limit over many uses of the channel)\, but it reduces to a single-letter 
 expression for at least three channels: the completely depolarizing channe
 l\, the quantum erasure channel\, and the qubit dephasing channel. We also
  show that isometric encoding is optimal for entanglement-assisted quantum
  channel.\n
LOCATION:MR15\, Centre for Mathematical Sciences
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