SPDC

A nonlinear process occurs inside nonlinear optical crystals where one photon with higher energy and wavevector is spontaneously down-converted into two photons with lower energy and wavevectors. In this process, both energy and momentum are conserved. In periodically and aperiodically poled nonlinear crystals (PPKTP, APKTP), the properties of the generated photons can be controlled by engineering the poling of the nonlinear crystals. SPDC allows the generation of pure heralded single photons and photon pairs exhibiting quantum correlations. These photons are important for various applications such as quantum key distribution, squeezed light generation, quantum computing, quantum super-resolution detection and imaging, etc.