An Equivalence Between Compatibility and Deterministic Underlying States in Quantum Mechanics

This paper establishes an equivalence between the pairwise compatibility of all observables in a scenario, and our ability to create a deterministic underlying-state model for that scenario (a type of hidden-variable model, typically used in the contextuality and nonlocality literature, where quantum states are treated as probability measures over ``better-defined states''). We first argue that the quantum state update rule implies that underlying-state models must update their states in agreement with the rules of conditional probability. We then demonstrate that deterministic underlying-state models meeting this criterion exist if and only if the system's observables are pairwise compatible, which is equivalent to the theoretical predictions of sequential measurements being independent of measurement order.
Comment: 5+3 pages, no figures