Single-Photon Quantum Contextuality on a Chip

In classical physics, properties of objects exist independently of the context, i.e., whether and how measurementsare performed. Quantum physics showed this assumption to be wrong, and that Nature is indeed“contextual”. Contextuality hasbeen observed in the simplest physical systems, such as single particles, and plays fundamental roles in quantum computationadvantage. Here, we demonstrate for thefirst time quantum contextuality in an integrated photonic chip. The chip implementsdifferent combinations of measurements on a single photon delocalized on four distinct spatial modes, showing violations of aClauser−Horne−Shimony−Holt (CHSH)-like noncontextuality inequality. This paves the way to compact and portable devicesfor contextuality-based quantum-powered protocols