title: Nonperturbative coherent population trapping: an analytic model.
abstract: Coherent population trapping is shown to occur in a driven symmetric double-well potential in the strong-field regime. The system parameters have been chosen to reproduce the 0(-) <--> 3(+) transition of the inversion mode of the ammonia molecule. For a molecule initially prepared in its lower doublet we find that, under certain circumstances, the 3(+) level remains unpopulated, and this occurs in spite of the fact that the laser field is resonant with the 0(-) <--> 3(+) transition and intense enough so as to strongly mix the 0(+) and 0(-) ground states. This counterintuitive result constitutes a coherent population trapping phenomenon of nonperturbative origin which cannot be accounted for with the usual models.
authors.affiliation: Departamento de Física Fundamental II, Universidad de La Laguna, 38205La Laguna, Tenerife, Spain.
authors.forename: V
authors.initials: V
authors.lastname: Delgado
authors.forename: J M
authors.initials: JM
authors.lastname: Gomez Llorente