Controllable transitions among phase-matching conditions in a single nonlinear crystal

Entangled photon pairs are crucial resources for quantum information processing protocols. Via the process of spontaneous parametric down-conversion (SPDC), we can generate these photon pairs using bulk nonlinear crystals. Traditionally, the crystal is designed to satisfy specific type of phase-matching condition. Here, we report controllable transitions among different types of phase-matching in a single periodically poled potassium titanyl phosphate (PPKTP) crystal. By carefully selecting pump conditions, we can satisfy different phase-matching conditions. This allows us to observe first-order type-II, fifth-order type-I, third-order type-0, and fifth-order type-II SPDCs. The temperature-dependent spectra of our source were also analyzed in detail. Finally, we discussed the possibility of observing more than nine SPDCs in this crystal. Our work not only deepens the understanding of the physics behind phase-matching conditions, but also offers the potential for a highly versatile entangled biphoton source for quantum information research.