Upper continuity bound on the quantum quasi-relative entropy

Abstract

We provide an upper bound on the quasi-relative entropy in terms of the trace distance. The bound is derived for any operator monotone decreasing function and either mixed qubit or classical states. Moreover, we derive an upper bound for the Umegaki and Tsallis relative entropies in the case of any finite-dimensional states. The bound for the relative entropy improves the known bounds for some states in any dimensions larger than four. The bound for the Tsallis entropy improves the known bounds.