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Relating relative entropy, optimal transport and Fisher information: a quantum HWI inequality

Published version
Peer-reviewed

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Authors

Rouzé, Cambyse 
Datta, Nilanjana 

Abstract

Quantum Markov semigroups characterize the time evolution of an important class of open quantum systems. Studying convergence properties of such a semigroup, and determining concentration properties of its invariant state, have been the focus of much research. Quantum versions of functional inequalities (like the modified logarithmic Sobolev and Poincar'{e} inequalities) and the so-called transportation cost inequalities, have proved to be essential for this purpose. Classical functional and transportation cost inequalities are seen to arise from a single geometric inequality, called the Ricci lower bound, via an inequality which interpolates between them. The latter is called the HWI-inequality, where the letters I, W and H are, respectively, acronyms for the Fisher information (arising in the modified logarithmic Sobolev inequality), the so-called Wasserstein distance (arising in the transportation cost inequality) and the relative entropy (or Boltzmann H function) arising in both. Hence, classically, all the above inequalities and the implications between them form a remarkable picture which relates elements from diverse mathematical fields, such as Riemannian geometry, information theory, optimal transport theory, Markov processes, concentration of measure, and convexity theory. Here we consider a quantum version of the Ricci lower bound introduced by Carlen and Maas, and prove that it implies a quantum HWI inequality from which the quantum functional and transportation cost inequalities follow. Our results hence establish that the unifying picture of the classical setting carries over to the quantum one.

Description

Keywords

quant-ph, quant-ph, math-ph, math.FA, math.MP

Journal Title

Annales Henri Poincaré

Conference Name

Journal ISSN

1424-0637
1424-0661

Volume Title

21

Publisher

Springer Science and Business Media LLC
Sponsorship
Munich Center for Quantum Science and Technology (DFG cluster of excellence 2111)