Efficiency limitation for realizing an atom-molecule adiabatic transfer based on a chainwise system

In a recent work, we have developed a robust chainwise atom-molecule adiabatic passage scheme to produce ultracold ground-state molecules via photo-associating free atoms [Phys. Rev. A 81, 013632 (2010)]. With the help of intermediate auxiliary levels, the pump laser intensity requested in the atomic photo-association process can be greatly reduced. In the present work, we extend the scheme to a more generalized (2n + 1)-level system and investigate its efficiency limitations. As the intermediate levels and auxiliary lasers increase, the atom-molecule adiabatic passage would be gradually closed, leading to a poor transfer efficiency. For the purpose of enhancing the efficiency, we present various optimization approaches to the laser parameters, involving order number n, relative strength ratio, and absolute strength.We show that there can remain a limit on the population transfer efficiency given by a three-level Λ system. In addition, we illustrate the importance of selecting an appropriate number of intermediate levels for maintaining a highly efficient transfer under mild experimental conditions.