Mechanism behind minimum-output-entropy nonadditivity

Identify a transparent mathematical mechanism explaining why quantum channels exhibit nonadditivity of minimum output entropy beyond the concentration-of-measure argument establishing existence.

Background

The paper distinguishes the known existence of finite-dimensional counterexamples from the unresolved task of explaining the phenomenon structurally. Although the paper develops a free-probabilistic and permutation-based framework, it does not claim that this fully identifies a transparent underlying mechanism for nonadditivity.