Quantum entanglement by Spontaneous Parametric Down-Conversion (SPDC) and the probability of correlated behavior

SPDC is a process commonly used in quantum optics to produce entangled photon pairs. It typically occurs in a nonlinear optical material (such as a beta barium borate (BBO) crystal), where a single high-energy photon (like a laser photon) interacts with the crystal and is down-converted into two lower-energy photons. These photons are often entangled in terms of properties like polarization, momentum, or phase.We also determine the probability of their entanglement and correlated behavior.