Applying the combination of the master and stochastic differential equations, we investigate in detail a continuous-variable entanglement of the twin beam generated by the coherent beat laser containing a parametric amplifier and coupled to thermal light of an external environment. The dipole-forbidden transition of the three-level atoms are coupled by the initial coherent superposition and classical pumping light emerging from the parametric oscillator. The atomic coherence induced by the classical pumping field and the initial coherent superposition induce a strong correlation between the two-mode radiation, which results in a high degree of the photon entanglement. In addition, the parametric amplifier enhances the achievable degree of entanglement of the two-mode fields. On the other hand, thermal light appears to degrade entanglement but a strong photon entanglement can be generated by managing the amount of thermal noise entering into the laser cavity through the output mirror.

应用主微分方程和随机微分方程的组合，我们详细研究了由包含参量放大器并耦合到外部环境的热光的相干差拍激光器产生的双光束的连续可变纠缠。三级原子的偶极子禁态跃迁通过初始相干叠加和从参量振荡器发出的经典泵浦光耦合在一起。由经典泵浦场引起的原子相干和初始相干叠加会引起双模辐射之间的强相关性，从而导致高度的光子纠缠。另外，参量放大器增强了双模场可达到的纠缠度。另一方面，