Classical microwaves as a universal model system for quantum contextuality

D. Frustaglia^a, J.P. Baltanás^a, M.C. Velázquez^b, A. Fernández^b, V. Losada^b, M. Freire^b, and A. Cabello^a

^aDepartamento de Física Aplicada II, Universidad de Sevilla, Spain

^bDepartamento de Electrónica y Electromagnetismo, Universidad de Sevilla, Spain.

Contextuality, a far-reaching generalization of nonlocality, stands out as a necessary resource for fault-tolerant quantum computation and other quantum-information tasks. Still, contextuality itself is not a signature of quantumness, since it can be simulated by classical models at the cost of extra memory. So far, these models are created ad hoc for each contextuality proof. This raises the question of whether quantum contextuality can be universally simulated with classical systems. Here we show [1] that classical electromagnetic waves provide a universal model for quantum contextuality in experiments with sequential measurements in which intermediate outcomes are stored in extra degrees of freedom. We support this by presenting experimental evidence of the state-independent violation of the Peres-Mermin noncontextuality inequality and the state-dependent violation of the noncontextuality version of Mermin's inequality with classical microwaves at the frequency used in consumer ovens. This is based upon the detection of intensity correlations under the assumption that intensities are ultimately due to a succession of individual events. Our results coincide with those found in quantum tests with ions, photons and neutrons. Unlike ad hoc classical contextual models, classical electromagnetism emerges as a universal model revealing the precise location of the memory needed to generate contextual outcomes and the mechanism to do it: the relative phase of the electromagnetic field in the extra degrees of freedom storing the intermediate outcomes. The principles explaining the bounded nature of contextuality and nonlocality in quantum theory are then tied to the question of why classical electromagnetism, under proper tests, is equally bounded.

[1] D. Frustaglia, J.P. Baltanás, M.C. Velázquez, A. Fernández, V. Lozada, M. Freire and A. Cabello, preprint (2014).