Formulation of Leggett-Garg inequalities in terms of $q$-entropies

Abstract

As is well known, the macroscopic realism and the noninvasive measurability together lead to Leggett-Garg inequalities violated by quantum mechanics. We consider tests of the Leggett-Garg type with use of the $q$-entropies. For all $q\geq1$, quantum mechanics predicts violations of an entire family of $q$-entropic inequalities of the Leggett-Garg type. Violations are exemplified with a quantum spin-$s$ system. In general, entropic Leggett-Garg inequalities give only necessary conditions that some probabilistic model is compatible with the macrorealism in the broader sense. The presented $q$-entropic inequalities allow to widen a class of situations, in which an incompatibility with the macrorealism can be tested. In the considered example, both the strength and range of violations are somehow improved by varying $q$. We also examine $q$-entropic inequalities of the Leggett-Garg type in the case of detection inefficiencies, when the no-click event may occur in each observation. With the use of the $q$-entropic inequalities, the required amount of efficiency may be reduced.