EIT: Electromagnetically induced transparency
CPT: Coherent population trapping
When two resonant light fields (probe field and strong coupling field) are incident on an opaque material whose atoms are composing of Λ three-level system, absorption of the probe field is disappeared and probe field is transmitted.
Many researcher said that this phenomenon is due to quantum destructive interference between the two transition probability. By the strong coupling field, excited state is split to two quantum states (AC stark effect). So, transition by probe field is superposed between the split two quantum states.
Another researcher said that this phenomenon is due to coherent population trapping. Without coupling field, resonant probe field is absorbed by the opaque material. In this situation, population of the ground state and excited state is varied as Rabi frequency. But if applying strong coupling field to the material, population on excited state transits only to ground state which is corresponding to coupling field. So, there is no population on ground state which is corresponding to probe field. So, the material cannot absorb the probe field.
Other researcher said that frequency difference (microwave) between two sub-level ground states in Λ-three level system creates dark state. Because the dark state has no population, it cannot absorb the light fields.
What is a super ordinate concept? (EIT, CPT and dark state)
