📝 SummarXiv

Abstract

In quantum causality, local laboratories are typically assumed to be operationally independent, each free to choose its own reference frames. We ask whether such independence is compatible with nonclassical correlations, and address this question using the resource-theoretic framework. We formalize local gauge freedom on laboratory connections as a symmetry, and prove that any bipartite process covariant under this symmetry is causally separable. This result holds in arbitrary dimensions and applies both to marginals of multipartite quantum circuits and to general reductions across cuts. Because such covariance enforces a strict superselection rule, it explains why circuit-embeddable dynamics, such as the quantum switch, cannot violate bipartite causal inequalities, even asymptotically. Our analysis thus establishes that generating nonclassical causal correlations requires physical resources that break operational independence.