General mapping of multiqudit entanglement conditions to nonseparability indicators for quantum-optical fields

We show that any multiqudit entanglement witness leads to a nonseparability indicator for quantum optical fields, which involves intensity correlations. We get, e.g., necessary and sufficient conditions for intensity or intensity-rate correlations to reveal polarization entanglement. We also derive separability conditions for experiments involving multiport interferometers, now feasible with integrated optics. We show advantages of using intensity rates rather than intensities, e.g., a mapping of the Bell inequalities to ones for optical fields. The results have implication for studies of nonclassicality of "macroscopic" systems of undefined or uncontrollable number of "particles."