Quantum coherence serves as a crucial physical resource, with its quantification emerging as a focal point in contemporary research. Superadditivity constitutes one of the most fundamental attributes in characterizing the coherence distribution in multipartite quantum systems. In this paper, we provide a way to derive tighter superadditivity inequalities of [Formula: see text]-norm coherence measure for arbitrary multiqubit states. We present a category of superadditivity relations related to the [Formula: see text]th [Formula: see text] power of [Formula: see text]-norm coherence [Formula: see text] under certain conditions. Our results are better than the existing ones and are illustrated in detail with examples.
We employ a basic formalism from convex analysis to show a simple relation between the entanglement of formation
EF and the conjugate function
E∗ of the entanglement function
E(rho)=S(traceArho). We then consider the conjectured strong superadditivity of the entanglement of formation
EF(rho)geEF(rhoI)+EF(rhoII), where
rhoI and
rhoII are the reductions of
rho to the different Hilbert space copies, and prove that it is equivalent with subadditivity of
E∗. As an application, we show that strong superadditivity would follow from multiplicativity of the maximal channel output purity for all non-trace-preserving quantum channels, when purity is measured by Schatten
p-norms for
p tending to 1.