Coherence as entropy increment for Tsallis and Renyi entropies

Abstract: Relative entropy of coherence can be written as an entropy difference of the original state and the incoherent state closest to it when measured by relative entropy. The natural question is, if we generalize this situation to Tsallis or R\'enyi entropies, would it define good coherence measures? In other words, we define a difference between Tsallis entropies of the original state and the incoherent state closest to it when measured by Tsallis relative entropy. Taking R\'enyi entropy instead of the Tsallis entropy, leads to the well-known distance-based R\'enyi coherence, which means this expression defined a good coherence measure. Interestingly, we show that Tsallis entropy does not generate even a genuine coherence monotone, unless it is under a very restrictive class of operations. Additionally, we provide continuity estimates for both Tsallis and R\'enyi coherence expressions. Furthermore, we present two coherence measures based on the closest incoherent state when measures by Tsallis or R\'enyi relative entropy.