We present an experimental state-independent violation of an inequality for noncontextual theories on single particles. We show that 20 different single-photon states violate an inequality which involves correlations between results of sequential compatible measurements by at least 419 standard deviations. Our results show that, for any physical system, even for a single system, and independent of its state, there is a universal set of tests whose results do not admit a noncontextual interpretation. This sheds new light on the role of quantum mechanics in quantum information processing.
@article{arxiv.0907.4494,
title = {State-independent quantum contextuality with single photons},
author = {Elias Amselem and Magnus Radmark and Mohamed Bourennane and Adan Cabello},
journal= {arXiv preprint arXiv:0907.4494},
year = {2009}
}