"Squashed entanglement": An additive entanglement measure

M Christandl, AJ Winter

Research output: Contribution to journalArticle (Academic Journal)peer-review

300 Citations (Scopus)


In this paper, we present a new entanglement monotone for bipartite quantum states. Its definition is inspired by the so-called intrinsic information of classical cryptography and is given by the halved minimum quantum conditional mutual information over all tripartite state extensions. We derive certain properties of the new measure which we call "squashed entanglement": it is a lower bound on entanglement of formation and an upper bound on distillable entanglement. Furthermore, it is convex, additive on tensor products, and superadditive in general. Continuity in the state is the only property of our entanglement measure which we cannot provide a proof for. We present some evidence, however, that our quantity has this property, the strongest indication being a conjectured Fannes-type inequality for the conditional von Neumann entropy. This inequality is proved in the classical case. (C) 2004 American Institute of Physics.
Translated title of the contribution"Squashed entanglement": An additive entanglement measure
Original languageEnglish
Pages (from-to)829 - 840
JournalJournal of Mathematical Physics
Volume45 (3)
Publication statusPublished - Mar 2004

Bibliographical note

Publisher: Amer Inst Physics
Other identifier: IDS Number: 773VX


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