Highly Efficient Creation and Detection of Ultracold Deeply-Bound Molecules via Chainwise Stimulated Raman Shortcut-to-Adiabatic Passage

Chainwise stimulated Raman adiabatic passage (C-STIRAP) in M-type molecular system is a good alternative in creating ultracold deeply-bound molecules when the typical STIRAP in Λ-type system does not work due to weak Frank-Condon factors between states. However, its creation efficiency under the smooth evolution is generally low. During the process, the population in the intermediate states may decay out quickly and the strong laser pulses may induce multi-photon processes. In this paper, we find that shortcut-to-adiabatic (STA) passage fits very well in improving the performance of the C-STIRAP. Currently, related discussions on the so-called chainwise stimulated Raman shortcut-to-adiabatic passage (C-STIRSAP) are rare. Here, we investigate this topic under the adiabatic elimination. Given a relation among the four incident pulses, it is quite interesting that the M-type system can be generalized into an effective Λ-type structure with the simplest resonant coupling. Consequently, all possible methods of STA for three-state system can be borrowed. We take the counter-diabatic driving and "chosen path" method as instances to demonstrate our treatment on the molecular system. Although the "chosen path" method does not work well in real three-state system if there is strong decay in the excited state, our C-STIRSAP protocol under both the two methods can create ultracold deeply-bound molecules with high efficiency in the M-type system. The evolution time is shortened without strong laser pulses and the robustness of STA is well preserved. Finally, the detection of ultracold deeply-bound molecules is discussed.