Key points are not available for this paper at this time.
A two-photon correlation experiment that was proposed by Franson Phys. Rev. Lett.62, 2205 ( 1989) and was recently carried out is analyzed in terms of electromagnetic waves in order to see whether the observed fourth-order interference effects can be explained classically. The conclusion is that, although a classical field can give rise to such interference effects, no classical field can actually account for the observations reported.
Ou et al. (1990) studied this question.