Shifting the Quantum-Classical Boundary: Theory and Experiment for Statistically Classical Optical Fields

TL;DR

This paper demonstrates that classical optical fields can exhibit Bell inequality violations similar to quantum systems, challenging traditional views on the quantum-classical boundary and suggesting a reinterpretation of it.

Contribution

It provides experimental evidence that classical optical fields can violate Bell inequalities, blurring the line between quantum and classical correlations.

Findings

Bell parameter exceeds 2.54, well beyond classical limit

Results align with classical theoretical predictions

Close to the quantum Tsirelson limit

Abstract

The growing recognition that entanglement is not exclusively a quantum property, and does not even originate with Schr\"odinger's famous remark about it [Proc. Camb. Phil. Soc. 31, 555 (1935)], prompts examination of its role in marking the quantum-classical boundary. We have done this by subjecting correlations of classical optical fields to new Bell-analysis experiments, and report here values of the Bell parameter greater than ${\cal B} = 2.54$. This is many standard deviations outside the limit ${\cal B} = 2$ established by the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality [Phys. Rev. Lett. 23, 880 (1969)], in agreement with our theoretical classical prediction, and not far from the Tsirelson limit ${\cal B} = 2.828...$. These results cast a new light on the standard quantum-classical boundary description, and suggest a reinterpretation of it.