Evading thermal population influence on enantiomeric-specific state transfer based on a cyclic three-level system via ro-vibrational transitions

Optical methods of enantiomeric-specific state transfer had been proposed theoretically based on a cyclic three-level system of chiral molecules. According to these theoretical methods, recently the breakthrough progress has been reported in experiments (Eibenberger et al 2017 Phys. Rev. Lett. 118 123002; Pérez et al 2017 Angew. Chem. Int. Ed. 56 12512) for cold gaseous chiral molecules but with achieving low state-specific enantiomeric enrichment. One of the limiting factors is the influence of the thermal population in the selected cyclic three-level system based on purely rotational transitions in the experiments. Here, we theoretically explore the improvement of the enantiomeric-specific state transfer at finite temperature by introducing ro-vibrational transitions for the cyclic three-level system of chiral molecules. Then, at the typical experimental temperature, approximately only the lowest state in the desired cyclic three-level system is thermally occupied and the optical method of enantiomeric-specific state transfer works well. Comparing with the case of purely rotational transitions where all the three states are thermally occupied, this modification will remarkably increase the obtained state-specific enantiomeric enrichment with enantiomeric excess being approximately 100%.