Abstract
We report the observation of two additional sub-natural line width quantum interference in the D₂ manifold of ³⁹K vapor, in addition to the usual single Electromagnetically induced transparency peak. The other two features appear exclusively because ³⁹K ground hyperfine splitting is smaller than the Doppler broadened absorption profile. This allows probe and control beams to swap their transition pathways. The control beam detuning captures the nature of the coherence, therefore an unusual phenomenon of conversion from perfect transparency to enhanced absorption is observed and explained by utilizing adiabatic elimination of the excited state in the Master equation. Controlling such dark and bright resonances leads to new applications in quantum technologies viz. frequency offset laser stabilization and long-lived quantum memory.