Tsirelson's bound from a generalized data processing inequality

Abstract

The strength of quantum correlations is bounded from above by Tsirelson's bound. We establish a connection between this bound and the fact that correlations between two systems cannot increase under local operations, a property known as the data processing inequality (DPI). More specifically, we consider arbitrary convex probabilistic theories. These can be equipped with an entropy measure that naturally generalizes the von Neumann entropy, as shown recently in Short and Wehner (2010 New J. Phys.12 033023) and Barnum et al (2010 New J. Phys.12 033024). We prove that if the DPI holds with respect to this generalized entropy measure then the underlying theory necessarily respects Tsirelson's bound. We, moreover, generalize this statement to any entropy measure satisfying certain minimal requirements. A consequence of our result is that not all the entropic relations used for deriving Tsirelson's bound via information causality in Pawlowski et al (2009 Nature461 1101–4) are necessary.