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Role of dressed-state interference in electromagnetically induced transparency

Electromagnetically induced transparency (EIT) in three-level systems uses a strong control laser on one transition to modify the absorption of a weak probe laser on a second transition. The control laser creates dressed states whose decay pathways show interference. We study the role of dressed-state interference in causing EIT in the three types of three-level systems -- lambda ($Λ$), ladder ($Ξ$), and vee (V). In order to get realistic values for the linewidths of the energy levels involved, we consider appropriate hyperfine levels of $^{87}$Rb. For such realistic systems, we find that dressed-state interference causes probe absorption---given by the imaginary part of the susceptibility---to go to zero in a $Λ$ system, but plays a negligible role in $Ξ$ and V systems.