Two-Photon Interference Constructed by Two Hong–Ou–Mandel Effects in One Mach-Zehnder Interferometer**Supported by the National Key R&D Program of China under Grant Nos 2017YFA0303800 and 2017YFA0303700, the National Natural Science Foundation of China under Grant Nos 11534006, 11774183 and 11674184, the Natural Science Foundation of Tianjin under Grant No 16JCZDJC31300, and the Collaborative Innovation Center of Extreme Optics.

Abstract

We present a two-photon interference experiment in a modified Mach-Zehnder (MZ) interferometer in which two Hong–Ou–Mandel effects occur in tandem and construct superposed two-photon states. The signal photons pass both the arms of the MZ interferometer while the idler photons pass one arm only. Interestingly, the probability of the idler photons emerging from any output port still shows a sine oscillation with the two-photon phase difference and it can be characterized only by the indistinguishability of the two-photon amplitudes. We also observe a two-photon interference pattern with a period being equal to the wavelength of the parametric photons instead of the two-photon photonic de Broglie wavelength due to the presence of two-photon phase difference, in particular, with complementary probabilities of finding the two-photon pairs in two output ports. The abundant observations can facilitate a more comprehensive understanding of the two-photon interference.