Dephrasure Channel and Superadditivity of Coherent Information

Felix Leditzky, Debbie Leung, Graeme Smith

Research output: Contribution to journalArticlepeer-review


The quantum capacity of a quantum channel captures its capability for noiseless quantum communication. It lies at the heart of quantum information theory. Unfortunately, our poor understanding of nonadditivity of coherent information makes it hard to understand the quantum capacity of all but very special channels. In this Letter, we consider the dephrasure channel, which is the concatenation of a dephasing channel and an erasure channel. This very simple channel displays remarkably rich and exotic properties: we find nonadditivity of coherent information at the two-letter level, a substantial gap between the threshold for zero quantum capacity and zero single-letter coherent information, a big gap between single-letter coherent and private information, and positive quantum capacity for all complementary channels. Its clean form simplifies the evaluation of coherent information substantially and, as such, we hope that the dephrasure channel will provide a much-needed laboratory for the testing of new ideas about nonadditivity.

Original languageEnglish (US)
Article number160501
JournalPhysical review letters
Issue number16
StatePublished - Oct 17 2018
Externally publishedYes

ASJC Scopus subject areas

  • General Physics and Astronomy


Dive into the research topics of 'Dephrasure Channel and Superadditivity of Coherent Information'. Together they form a unique fingerprint.

Cite this