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Register a new userNaturally restricted subsets of nonsignaling correlations: typicality and convergence
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It is well-known that in a Bell experiment, the observed correlation between measurement outcomes -- as predicted by quantum theory -- can be stronger than that allowed by local causality, yet not fully constrained by the principle of relativistic causality. In practice, the characterization of the set Q of quantum correlations is often carried out through a converging hierarchy of outer approximations. On the other hand, some subsets of Q arising from additional constraints [e.g., originating from quantum states having positive-partial-transposition (PPT) or being finite-dimensional maximally entangled] turn out to be also amenable to similar numerical characterizations. How then, at a quantitative level, are all these naturally restricted subsets of nonsignaling correlations different? Here, we consider several bipartite Bell scenarios and numerically estimate their volume relative to that of the set of nonsignaling correlations. Among others, our findings allow us to (1) gain insight on (i) the effectiveness of the so-called Q1 and the almost quantum set in approximating Q, (ii) the rate of convergence among the first few levels of the aforementioned outer approximations, (iii) the typicality of the phenomenon of more nonlocality with less entanglement, and (2) identify a Bell scenario whose Bell violation by PPT states might be experimentally viable.
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Many three-party correlations, including some that are commonly described as genuinely tripartite nonlocal, can be simulated by a network of underlying subsystems that display only bipartite nonsignaling nonlocal behavior. Quantum mechanics predicts three-party correlations that admit no such simulation, suggesting there a
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