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Data processing for the sandwiched Rényi divergence: a condition for equality

dc.creatorLeditzky, Felix
dc.creatorRouzé, Cambyse
dc.creatorDatta, Nilanjana
dc.date.accessioned2016-08-23
dc.date.accessioned2018-11-24T23:26:57Z
dc.date.available2016-10-31T10:42:54Z
dc.date.available2018-11-24T23:26:57Z
dc.date.issued2016
dc.identifierhttps://www.repository.cam.ac.uk/handle/1810/260960
dc.identifier.urihttp://repository.aust.edu.ng/xmlui/handle/123456789/3919
dc.description.abstractThe $\alpha$-sandwiched Rényi divergence satisfies the data processing inequality, i.e. monotonicity under quantum operations, for $\alpha$ $\geq$ 1/2. In this article, we derive a necessary and sufficient algebraic condition for equality in the data processing inequality for the $\alpha$-sandwiched Rényi divergence for all $\alpha$ $\geq$ 1/2. For the range $\alpha$ $\in$ [1/2,1), our result provides the first condition for equality obtained thus far. To prove our result, we first consider the special case of partial trace, and derive a condition for equality based on the original proof of the data processing inequality by Frank and Lieb [17] using a strict convexity/concavity argument. We then generalize to arbitrary quantum operations via the Stinespring Representation Theorem. As applications of our condition for equality in the data processing inequality, we deduce conditions for equality in various entropic inequalities. We formulate a Rényi version of the Araki-Lieb inequality and analyze the case of equality, generalizing a result by Carlen and Lieb [9] about equality in the original Araki-Lieb inequality. Furthermore, we prove a general lower bound on a Rényi version of the entanglement of formation, and observe that it is attained by states saturating the Rényi version of the Araki-Lieb inequality. Finally, we prove that the known upper bound on the entanglement fidelity in terms of the usual fidelity is saturated only by pure states.
dc.languageen
dc.publisherSpringer
dc.publisherLetters in Mathematical Physics
dc.subjectrelative entropies
dc.subjectRényi entropies
dc.subjectdata processing inequality
dc.subjectequality condition
dc.subjectconditional entropy
dc.subjectentanglement of formation
dc.titleData processing for the sandwiched Rényi divergence: a condition for equality
dc.typeArticle


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