The Structure of Shared Classical Facts in Quantum Systems

Abstract

Perfectly matching local outcomes need not constitute a nondisturbing shared classical record. For finite-dimensional multipartite states, we prove that nontrivial exact records are equivalent to a spectrum sharing structure with a unique finest decomposition into locally distinguishable sectors, where entanglement may persist. For a fixed complete pointer, exact sharing is equivalent to strong quantum Darwinism together with global nondisturbance, while spectrum broadcast structure additionally requires conditional independence. Arbitrarily weak full-rank admixtures eliminate exact sharing, but two-sided distance bounds quantify robustness through disturbance and disagreement, while information bounds connect accurate local readouts to observer consensus.