Superadditivity of Private Information for Any Number of Uses of the Channel

David Elkouss, Sergii Strelchuk

Research output: Contribution to journalArticleScientificpeer-review

17 Citations (Scopus)


The quantum capacity of a quantum channel is always smaller than the capacity of the channel for private communication. Both quantities are given by the infinite regularization of the coherent and the private information, respectively, which makes their evaluation very difficult. Here, we construct a family of channels for which the private and coherent information can remain strictly superadditive for unbounded number of uses, thus demonstrating that the regularization is necessary. We prove this by showing that the coherent information is strictly larger than the private information of a smaller number of uses of the channel. This implies that even though the quantum capacity is upper bounded by the private capacity, the nonregularized quantities can be interleaved.

Original languageEnglish
Article number040501
Pages (from-to)1-5
Number of pages5
JournalPhysical Review Letters
Issue number4
Publication statusPublished - 20 Jul 2015


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