positive P-representation

Quantum antibunching, vital for single-photon sources, enables applications in quantum technology, such as secure communication and quantum computing.  This study investigates photon antibunching generation in a Nonlinear coupler (NLC) comprising two coupled waveguides: one linear and one with the second-order nonlinearity.  Each waveguide is excited by a coherent laser source, with the second harmonic generation enhancing antibunching.  Using the Schrödinger picture, the system's Hamiltonian is transformed into a master equation via the Liouville–von Neumann equation.