Fig. 1: Nonlocality scenarios.
a Causal structure for the standard Bell scenario, in which a classical resource λAB is shared between two parties. λAB is responsible for the observed joint correlations of measurement outcomes a and b given inputs x and y, respectively. b Broadcast scenario with three parties, where a classical bipartite resource λAB is shared between one party and a broadcast channel ΩBC. Measurement nodes receive inputs x, y and z, respectively, yielding outcomes a, b and c. The broadcast parties are subject only to no-signaling (NS) constraints. c, d Schematic representation of the membership of quantum states within different correlation sets for the bipartite Bell (c), and tripartite broadcast (d) scenarios. Bell-NL (Br-NL) signify Bell-nonlocal (broadcast-nonlocal) correlations; states in the Bell-L (Br-L) set are Bell-local (broadcast-local), admitting a local hidden variable in their respective scenario. The intermediate yellow region in (d) represents the set of Bell-local states that can be activated in the broadcast scenario.
