Figure 1:
Different experiments can be used to test nonlocality. In each case, a source S distributes the two parts of an entangled state ρ_{AB} to two measuring devices. The measuring devices are provided with instructions on what measurement to perform. The measuring device then provides a classical output, symbolized here by which light bulb—green or red—lights up. (a) In the standard Bell scenario, the instructions to the measurement devices are classical [3]. The state exhibits nonlocality if the correlations between measurement settings and measurement results violate a Bell inequality. (b) In the scenario considered by Masanes, Liang, and Doherty [8], the instructions are classical, as in the standard Bell scenario, but the measurement apparatuses have access to an auxiliary entangled state σ_{AB}. This scenario enables the “activation” of hidden nonlocality. (c) In the semiquantum scenario introduced by Buscemi [4], the instructions i and j fed to the detectors are encoded in quantum systems described by quantum states σ_{A}^{i} and σ_{B}^{j}. Appropriate choice of the states σ_{A}^{i} and σ_{B}^{j} can produce nonlocal correlations for all entangled states ρ_{AB}.