Fig. 3
From: Experimental demonstration of robust self-testing for bipartite entangled states
Self-testing results for four groups of two-qubit states. For each subgraph, we experimentally generate a two-qubit state ρj (j = 0, 1, 2, 3), which is supposed to be a pure target state |φtarget(θj)〉 which maximally violates a certain inequality β(αj). To each ρj, three unitary local operators are applied, resulting in a series of tested states ρj(k)(k = 0, 1, 2), which can be self-tested by measuring the violation of β(αj). A self-testing bound, which describes the minimum possible fidelity to |φtarget(θj)〉, is plotted as the function of the violation of β(αj) (the solid line). Therefore, corresponding to the measured violation for each tested state, in theory there exists a minimum possible fidelity FS, as labeled by the blue square on the self-testing bound. In order to verify the reliability of this self-testing protocol, the density matrix of ρj(k) is reconstructed through a state tomography process, and its actual fidelity FT to |φtarget(θj)〉 (labeled by red circles) is well above FS. The insets show partial enlarged details of the data points
