  Enantio-conversion of chiral mixtures, converting the mixtures composed of
left- and right-handed chiral molecules into the homochiral ensembles, has
become an important research topic in chemical and biological fields. In
previous studies on enantio-conversion, the tunneling interaction between the
left- and right-handed chiral states was often neglected. However, for certain
chiral molecules, this tunneling interaction is significant and cannot be
ignored. Here we propose a scheme for enantio-conversion of chiral mixtures
through optical pumping based on a four-level model of chiral molecules,
comprising two chiral ground states and two achiral excited states, with a
tunneling interaction between the chiral states. Under one-photon large
detuning and two-photon resonance conditions, one of the achiral excited states
is eliminated adiabatically. By well designing the detuning and coupling
strengths of the electromagnetic fields, the tunneling interaction between two
chiral states and the interaction between one of the chiral states and the
remaining achiral excited state can be eliminated. Consequently, one chiral
state remains unchanged, while the other can be excited to an achiral excited
state, establishing chiral-state-selective excitations. By numerically
calculating the populations of two chiral ground states and the enantiomeric
excess, we observe that high-efficiency enantio-conversion is achieved under
the combined effects of system dissipation and chiral-state-selective
excitations.
