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. These classes are distinguished by which operational identities are enforced, where certain natural subsets form a hierarchy and provide a new way to understand and classify different forms of quantum correlations. Specifically, we show that violations of inequalities at different levels of this hierarchy can serve as witnesses to determine whether a bipartite quantum state exhibits entanglement, steering, or nonlocality, thereby giving a systematic and unified method for certifying these distinct bipartite quantum resources. To illustrate the power of this approach, we demonstrate the violation of one such inequality in an experiment with polarization-entangled photons. This experimental implementation enables us to certify entanglement in certain two-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, and it is able to certify {\em any} entangled state without requiring any auxiliary entangled sources.

Personal information

Yujie Zhang is a postdoctoral researcher at the Institute for Quantum Computing (IQC), University of Waterloo, and also affiliated with the Perimeter Institute. Yujie received his PhD from the University of Illinois at Urbana–Champaign. His research lies at the intersection of photonic quantum information and quantum foundations, with a focus on understanding nonclassical features of quantum mechanics through concepts from quantum foundations, and on applying these ideas to the design of novel photonic quantum protocols.

Reference

https://arxiv.org/abs/2507.01122