Time control of two-photon interference

The interference of photons with the same polarization generated by spontaneous parametric down conversion in a Hong-Ou-Mandel interferometer, after one of them passed through a symmetric cavity, is demonstrated experimentally. In the regime where the cavity length is larger than the one-photon coherence length, photon coalescence and anticoalescence interference is observed. We show that by changing the cavity length, coincidence peaks can be transformed in dips and vice versa, even though the coherence length of the photon wave packet is smaller than the cavity length. The photon pair coalescence or anticoalescence at the beam splitter can be controlled by changing the length of the cavity