Qubit channels that achieve capacity with two states

Dominic W. Berry*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)
4 Downloads (Pure)


This paper considers a class of qubit channels for which three states are always sufficient to achieve the Holevo capacity. For these channels, it is known that there are cases where two orthogonal states are sufficient, two nonorthogonal states are required, or three states are necessary. Here a systematic theory is given which provides criteria to distinguish cases where two states are sufficient, and determine whether these two states should be orthogonal or nonorthogonal. In addition, we prove a theorem on the form of the optimal ensemble when three states are required, and present efficient methods of calculating the Holevo capacity.

Original languageEnglish
Article number032334
Pages (from-to)1-9
Number of pages9
JournalPhysical Review A - Atomic, Molecular, and Optical Physics
Issue number3
Publication statusPublished - 1 Mar 2005
Externally publishedYes

Bibliographical note

Berry DW, Phys. Rev. A. 71(3), 032334, 2005. Copyright 2005 by the American Physical Society. The original article can be found at http://dx.doi.org/10.1103/PhysRevA.71.032334.


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