Quantum Coordination without Conditioning under Restricted Information

TL;DR

This paper demonstrates that quantum systems, even with separable states, can achieve coordination tasks under restricted information that classical models cannot, highlighting a quantum advantage in information-limited scenarios.

Contribution

It shows that quantum discord and separable states enable coordination beyond classical limits without conditioning on past history.

Findings

Quantum systems overcome classical limitations in restricted information scenarios.

Separable states with quantum discord facilitate unattainable joint distributions.

Quantum models cannot fully replicate adaptive dependence on past outcomes.

Abstract

We study coordination under restricted information, where classical local models fail to implement certain correlated distributions because agents cannot condition on past history. We show that quantum systems overcome this limitation even when using only separable states. Both classically diagonal encodings (shared latent variables) and separable states with noncommuting local structure (quantum discord) enable the implementation of joint distributions that are unattainable by any classical local rules under the same information constraints. The quantum advantage arises from enabling latent-variable coordination without requiring agents to condition on the latent variable itself -- a construction that succeeds where no classical local model can. Separable states with nonzero quantum discord provide an alternative mechanism for realizing such coordination. At the same time, quantum models remain strictly limited by the information structure: unlike perfect recall, they cannot reproduce fully adaptive dependence on realized past outcomes that are observationally indistinguishable. Thus, quantum correlations serve as a partial substitute for perfect recall.