Key points are not available for this paper at this time.
A two-photon coincidence experiment of the kind recently proposed by J. D. Franson Phys. Rev. Lett. 62, 2205 (1989) has been carried out with signal and idelr photons produced in the process of parametric down-conversion. The coincidence rate registered by the two detectors is found to exhibit a cosine variation with the optical path difference, with periodicity equal to the wavelength.
Ou et al. (Mon,) studied this question.