Shifting the quantum-classical boundary: Theory and experiment for statistically classical optical fields

The growing recognition that entanglement is not exclusively a quantum property, and does not even originate with Schrödinger’s famous remark about it [Proc. Cambridge Philos. Soc. 31, 555 (1935)], prompts the 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 B = 2.54. This is many standard deviations outside the limit B = 2 established by the Clauser–Horne–Shimony–Holt Bell inequality [Phys. Rev. Lett. 23, 880 (1969)], in agreement with our theoretical classical prediction, and not far from the Tsirelson limit B = 2.828…. These results cast a new light on the standard quantum-classical boundary description, and suggest a reinterpretation of it.