The Experimental Investigation of Filter Effect on Visibility of Fringes in Quantum Single Photon Interferometry

This study investigates the effect of the filter on the visibility of fringes in single-photon interference. A pair of photons by spontaneous parametric down-conversion is produced using a nonlinear crystal. One of them passes through a Mach-Zehnder interferometer due to the principle of indistinguishability of the paths, which interferes with itself. By changing the length of the paths of the Mach-Zehnder arms with the help of a stage, the interference happens in the coincidence pattern. In order to align the optical elements and minimize the optical path difference in the interferometer arms, interferometry with laser and white light has been used before single photon interferometry. By placing filters with different bandwidths in the signal and idler photons path, we see interference fringes with different visibility. An interference pattern is obtained by recording the coincidence between the correlated photons. The results show that the frequency bandwidth of filters affects the coherence length of generated photons and so the visibility of interference fringes.