Quantum accessible information and classical entropy inequalities

Abstract: Computing accessible information for an ensemble of quantum states is a basic problem in quantum information theory. The optimality criterion recently obtained in [7], when applied to specific ensembles of states, leads to nontrivial tight lower bounds for the Shannon entropy that are discrete relatives of the famous log-Sobolev inequality. In this light, the hypothesis of globally information-optimal measurement for an ensemble of equiangular equiprobable states (quantum pyramids) put forward and numerically substantiated in [2] is reconsidered and the corresponding tight entropy inequalities are proposed. We prove these inequalities in the cases of state ensembles corresponding to acute or flat pyramids, thus providing the proof of the hypothesis concerning the globally information-optimal observable.