No Bipartite-Nonlocal Causal Theory Can Explain Nature's Correlations

Abstract: We show that some tripartite quantum correlations are inexplicable by any causal theory involving bipartite nonclassical common causes and unlimited shared randomness. This constitutes a device-independent proof that Nature's nonlocality is fundamentally at least tripartite in every conceivable physical theory - no matter how exotic. To formalize this claim we are compelled to substitute Svetlichny's historical definition of genuine tripartite nonlocality with a novel theory-agnostic definition tied to the framework of Local Operations and Shared Randomness (LOSR). A companion article [PRA. 104, 052207 (2021)] generalizes these concepts to any number of parties, providing experimentally amenable device-independent inequality constraints along with quantum correlations violating them, thereby certifying that Nature's nonlocality must be boundlessly multipartite.