Multiphoton EP control with multidressing fields and linear-nonlinear competition in natural energy level systems

One-step generation of W-state entangled three-photons based on spontaneous six-wave mixing (SSWM) has been shown to have significant advantages over cascaded spontaneous parametric down conversion (SPDC) methods and cascaded spontaneous four-wave mixing (SFWM) methods. On this basis, this paper provides a theoretical insight into the optical response in non-Hermitian SSWM systems under linear and nonlinear coupling effects. Among them, the linear process is mainly controlled by group velocity and decay rate, and the nonlinear process is mainly controlled by Rabi oscillation and detuning. In the nonlinear-dominated optical response process, the higher-order EP coupling is more obviously controlled by the intensity of the dressing field, thus providing insights into the PT symmetry breaking in energy-level systems based on the EIT principle. Further, in this paper, the modulation of SSWM by single dressing field and two double dressing fields is theoretically analyzed. Compared with the single dressing field, the higher-order EP coupling effect of the cascaded double dressing field and the nested double dressing field is more obvious, and the Rabi oscillatory coupling order is higher, and more cycles can be observed, which generates a high-dimensional information coherence channel and improves the coupling efficiency and strength. In addition, the coherence time of SSWM induced under the weak dressing field increases continuously during the transition from the linear optical response dominant process to the nonlinear optical response process dominant process, and multi-dressing modulation with stronger interactions between the dressing fields then balances the lifetimes of strong dressing and weak dressing entangled states. Which is of great significance for quantum information storage and communication.