Coherent population trapping in a dressed two-level atom via a   bichromatic field
  We show theoretically that by applying a bichromatic electromagnetic field, the dressed states of a monochromatically driven two-level atom can be pumped into a coherent superposition termed as dressed-state coherent population trapping. Such effect can be viewed as a new doorknob to manipulate a two-level system via its control over dressed-state populations. Application of this effect in the precision measurement of Rabi frequency, the unexpected population inversion and lasing without inversion are discussed to demonstrate such controllability. 
Peng Li, Qun Zhang, Xi-Jing Ning and J. Q. You