Figure 1

Figure 1: Different experiments can be used to test nonlocality. In each case, a source S distributes the two parts of an entangled state ρAB 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 σAB. 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 σAi and σBj. Appropriate choice of the states σAi and σBj can produce nonlocal correlations for all entangled states ρAB.