Inequalities and Separations Among Assisted Capacities of Quantum Channels

Charles H. Bennett, Igor Devetak, Peter W. Shor, and John A. Smolin
Phys. Rev. Lett. 96, 150502 – Published 18 April 2006

Abstract

We exhibit quantum channels whose classical and quantum capacities, when assisted by classical feedback, exceed their unassisted classical Holevo capacity. These channels are designed to be noisy in a way that can be corrected with the help of the output and a reference system entangled with part of the input. A similar construction yields quantum channels whose classical capacity, when assisted by two-way classical communication independent of the source, exceeds their classical capacity assisted by feedback alone. We give a hierarchy of capacity inequalities and open questions.

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  • Received 19 April 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.150502

©2006 American Physical Society

Authors & Affiliations

Charles H. Bennett1,*, Igor Devetak1,†, Peter W. Shor2,‡, and John A. Smolin1,§

  • 1IBM T. J. Watson Research Center, Yorktown Heights, New York 10598, USA
  • 2Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

  • *Electronic address: bennetc@watson.ibm.com
  • Electronic address: devetak@csi.usc.edu
  • Electronic address: shor@math.mit.edu
  • §Electronic address: smolin@watson.ibm.com

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Issue

Vol. 96, Iss. 15 — 21 April 2006

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