Figure 2
Results.
Measured values of (a) the bipartite entanglement witness 
, (b) the Svetlichny function 
and (c) its derivative 
as a function of β. The square dots show the measurements performed on the ground state; the red line shows the expected behaviors for the ideal ground state; the blue line represents the theoretical values for a state affected by noise. The vertical dotted line identifies the ‘critical point’ β = −1; the horizontal dashed line in (a) and (b) show the lowest (highest) possible value that can be achieved by 
(
) for a (bi-)separable state; and the full black horizontal line in (b) shows the highest value that can be achieved by a GHZ state. (d) Relation between 
and τ3 for the ground state |g3(β)〉. The dashed vertical line marks the local realistic bound imposed to the Svetlichny parameter. This identifies the threshold value τ3 = 0.25 above which the state is non-local in a tripartite sense. The (blue) circle-shaped points are the values of τ3 obtained using the analytic relation with 
discussed in the body of the paper, evaluated at the experimental values of the Svetlichny parameter. The (magenta) square-shaped data points are the values of τ3 estimated using local measurement settings. (e) Analogous plot for 
. In this case, the threshold for tripartite non-locality is 
. The same color-code used in panel (a) holds here. Error bars are determined by standard error propagation with Poissonian distributions attached to the experimental counts.
