All entangled states can be certified by a violation of noncontextuality inequalities

Abstract: By combining the assumption of Bell locality with that of generalized noncontextuality, we define different classes of noncontextuality inequalities for correlations in a bipartite Bell scenario, with the classes being distinguished by which set of operational identities are taken into account, with certain natural subsets defining a hierarchy of classes. We prove that violations of the inequalities at different levels of the hierarchy can witness that a bipartite state is entangled, steerable, or nonlocal, respectively, thereby providing a means of certifying these different forms of quantum correlations. To illustrate the power of this approach, we demonstrate the violation of one such inequality in an experiment with polarization-entangled photons. This allows us to certify entanglement in certain qubit isotropic states for which certification by Bell or steering inequalities is known to be impossible. Our entanglement certification scheme is the first to combine all of the following desirable features: it requires no prior characterization of the measurements, it delivers a verdict based on quantities that are independent of the tomographic gauge freedom, it is able to certify any entangled state, and it requires no auxiliary entangled sources.