Observation of quantum coherence by means of temporal Bell-type inequalities

Violation of temporal Bell inequalities, based on the premises of realism and non-invasive measurability, provides a criterion for exhibiting macroscopic quantum coherence. Although the experimental refutation of this kind of inequality is extremely difficult when macroscopic systems are involved, we can get some insight into the problem by studying systems at an intermediate scale. In this case, the non-invasive measurability assumption does not hold; the inhibition of dynamics for continuous monitoring (quantum Zeno effect) is one consequence of this. However, directly testable Bell-type inequalities can be derived if one replaces the non-invasive measurability assumption by a stationarity condition. Accordingly to a realist approach, such inequalities should hold for any (strictly) two-state stochastic process. Here we propose an experimental situation where violations of such inequalities may possibly be observed.