Dark resonance formation with magnetically-induced transitions: extension of spectral range and giant circular dichroism

Dark resonances were formed via electromagnetically induced transparency for the first time involving magnetically-induced $\mathrm{\Delta }F=\pm 2$ atomic transitions of alkali metal atom, which are forbidden at zero magnetic field. The probability of these transitions undergoes rapid growth when $300-3000$~G magnetic field is applied, allowing formation of dark resonances, widely tunable in the GHz range. It is established that for $\mathrm{\Delta }F=+2$ ($\Delta F =-2$)transition,thecouplinglasertunedto$\Delta F = +1$($\Delta F =-1$) transition of the hyperfine $\mathrm{\Lambda }$-system must be ${\sigma }^{+}$ (${\sigma }^{-}$) polarized, manifesting anomalous circular dichroism.