Monotones from multi-invariants: a classification

Abstract: In this paper we study local unitary invariants of a multi-partite quantum state that are monotonic, on average, under local operations and classical communication (locc). In particular we focus on local unitary invariants that are constructed out of polynomials in the state and its conjugate - called multi-invariants. Multi-invariants are labeled by certain types of graphs. Recently, in \cite{Gadde:2024jfi}, the authors related the condition of monotonicity under locc to a graph theoretic condition on the multi-invariant called edge-convexity. In this paper, we conjecture a complete classification of edge-convex multi-invariants. The conjecture states that the edge-convex multi-invariants are labeled by finite Coxeter groups. We prove this conjecture for all but six cases.