Superadditivity of the Classical Capacity with Limited Entanglement Assistance

Elton Yechao Zhu, Quntao Zhuang, Peter W. Shor

Research output: Contribution to journalArticlepeer-review

19 Scopus citations


Finding the optimal encoding strategies can be challenging for communication using quantum channels, as classical and quantum capacities may be superadditive. Entanglement assistance can often simplify this task, as the entanglement-assisted classical capacity for any channel is additive, making entanglement across channel uses unnecessary. If the entanglement assistance is limited, the picture is much more unclear. Suppose the classical capacity is superadditive, then the classical capacity with limited entanglement assistance could retain superadditivity by continuity arguments. If the classical capacity is additive, it is unknown if superadditivity can still be developed with limited entanglement assistance. We show this is possible, by providing an example. We construct a channel for which the classical capacity is additive, but that with limited entanglement assistance can be superadditive. This shows entanglement plays a weird role in communication, and we still understand very little about it.

Original languageEnglish (US)
Article number040503
JournalPhysical review letters
Issue number4
StatePublished - Jul 27 2017
Externally publishedYes

ASJC Scopus subject areas

  • General Physics and Astronomy


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