Experimental violation of a Bell-like inequality with optical vortex beams

TL;DR

This paper experimentally demonstrates that classical optical vortex beams with orbital angular momentum can violate a Bell-like inequality, revealing quantum-like entanglement properties in classical light fields, with violations increasing at higher angular momentum.

Contribution

The study provides the first experimental evidence of Bell inequality violation in classical optical vortex beams, linking topological singularities to quantum entanglement concepts.

Findings

Bell inequality violation increases with orbital angular momentum.

Negativity of Wigner function observed at the origin for LG10.

Positive Wigner function at the origin for LG20.

Abstract

Optical beams with topological singularities have a Schmidt decomposition. Hence, they display features typically associated with bipartite quantum systems; in particular, these classical beams can exhibit entanglement. This classical entanglement can be quantified by a Bell inequality formulated in terms of Wigner functions. We experimentally demonstrate the violation of this inequality for Laguerre-Gauss (LG) beams and confirm that the violation increases with increasing orbital angular momentum. Our measurements yield negativity of the Wigner function at the origin for $\LG_{10}$ beams, whereas for $\LG_{20}$ we always get a positive value.