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)PCPSA40008-198110.1017/S0305004100013554], 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)10.1103/PhysRevLett.23.880PRLTAO0031-9007], 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.