Contextuality Can be Verified with Noncontextual Experiments

TL;DR

This paper demonstrates that contextuality in quantum mechanics can be verified through experiments involving weak and projective measurements, linking it to the properties of Kirkwood-Dirac quasiprobability distributions.

Contribution

It introduces a method to verify quantum contextuality using noncontextual experiments based on KD distributions, connecting contextuality to measurable quasiprobabilities.

Findings

Contextuality is linked to non-KD-positive states.

A measurement scheme for KD distributions is proposed.

Noncontextual experiments can verify contextuality.

Abstract

We uncover new features of generalized contextuality by connecting it to the Kirkwood-Dirac (KD) quasiprobability distribution. Quantum states can be represented by KD distributions, which take values in the complex unit disc. Only for ``KD-positive'' states are the KD distributions joint probability distributions. A KD distribution can be measured by a series of weak and projective measurements. We design such an experiment and show that it is contextual iff the underlying state is not KD-positive. We analyze this connection with respect to mixed KD-positive states that cannot be decomposed as convex combinations of pure KD-positive states. Our result is the construction of a noncontextual experiment that enables an experimenter to verify contextuality.