An experimental test of noncontextuality without unphysical idealizations

• Published in: Nature communications Vol. 7; no. 1; pp. ncomms11780 - 7
• Main Authors: Mazurek, Michael D., Pusey, Matthew F., Kunjwal, Ravi, Resch, Kevin J., Spekkens, Robert W.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 13.06.2016; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/400/3925; 639/766/483/640; Causality; Experiments; Humanities and Social Sciences; multidisciplinary; Physics; Probability; Quantum theory; Science; Science (multidisciplinary); Waterloo Ontario Canada; Canada
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms11780

To make precise the sense in which nature fails to respect classical physics, one requires a formal notion of classicality. Ideally, such a notion should be defined operationally, so that it can be subject to direct experimental test, and it should be applicable in a wide variety of experimental scenarios so that it can cover the breadth of phenomena thought to defy classical understanding. Bell’s notion of local causality fulfils the first criterion but not the second. The notion of noncontextuality fulfils the second criterion, but it is a long-standing question whether it can be made to fulfil the first. Previous attempts to test noncontextuality have all assumed idealizations that real experiments cannot achieve, namely noiseless measurements and exact operational equivalences. Here we show how to devise tests that are free of these idealizations. We perform a photonic implementation of one such test, ruling out noncontextual models with high confidence. No noncontextual hidden-variable model can be consistent with quantum theory, but proving such an inconsistency with nature itself is a long-standing problem. Here, the authors devise experimentally-achievable tests of noncontextuality and perform a photonic implementation that rules out such models.