本文利用一个具有隧穿耦合效应的四能级结构模型来描述超冷铯原子制备超冷铯分子的过程,理论分析了受激拉曼绝热通道过程中的两激光脉冲参数对铯原子-分子转换效率的影响。结果表明,在原子-分子暗态条件下,通过双色光缔合利用双光子共振条件的最优化处理方法可以使转换效率提高到90％以上,并给出了两激光脉冲参数的最优化区间。另外,通过分析原子态和束缚分子基态上粒子数布居的动力学演化,给出了光场的最优化条件,只有适当的匹配两激光场的有效Rabi频率、延迟系数和脉冲宽度时,才能高效地实现超冷铯原子-分子的相干布居转换。

We study theoretically the Gaussian laser pump field and dump field conditions for producing ultracold cesium molecules from ultracold atomic condensates by the two-color photoassociation through the stimulated Raman adiabatic passage (STIRAP) in a tunneling four-level structure.An excited molecule |bk〉 is produced in an outer excited state from the ultracold atoms at the initial state |a〉 via the pump field.Then,the excited molecule |bk〉 is converted to the inner excited molecule |bv0〉by the tunneling coupling.Furthermore,the dump field drives |bv0〉 to the ground molecular state |g〉.In this progress,the detuning of pump field Δp is fixed at -(0.16 cm-1)32,and the detuning of dump field Δd is satisfied with the two-photon resonance condition,which can be obtained from the dark state solutions of the coupled mean-field equations.In the two-color photo association,we can control the two effective Rabi frequencies (Ω0p,Ω0d),the delay coefficient (α) and the width (T) of the two laser fields and obtain the high conversion efficiency (η≥0.9) as the optimum conditions of the pump and dump fields.In the meantime,the population dynamics of atoms and stable bound ground molecules with the conversion efficiency at 0.919 are investigated at specific parameters,where Ω0p=600×105 s-1、Ω0d=160×105 s-1、α=1.9、T=0.9×10-4 s.The unequal effective Rabi frequencies (Ω0p ≠Ω0d) are to the benefit of the coherent transfer from the atoms to the ground molecules through the STIRAP for the wide ranges of the delay coefficient and the width.Furthermore,we also investigate comparatively the cases of the small and large equal effective Rabi frequencies (Ω0p=Ω0d) for maintaining the delay coefficient and the width.The results have demonstrated that the conversion efficiencies are decreased sharply.Therefore,only the matched the effective Rabi frequencies,the delay coefficient and the width of the two laser fields can convert efficiently the ultracold atoms to the stable ground ultracold molecules.