Quantum antibunching in nonlinear couplers: a phase space approach using the 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. The master equation is further translated into a Fokker–Planck equation using the positive-P representation and subsequently mapped to stochastic differential equations via Ito rules for numerical analysis. The effects of input parameters on antibunching behavior are examined, showcasing the potential of simple systems like NLCs for precise single-photon manipulation, advancing quantum technology.