Competition of dark states: Optical resonances with anomalous magnetic field dependence

A different type of optical resonance has been observed in Doppler-free saturated absorption spectroscopy when the pump beam has elliptical polarization slightly deviating from the ${\sigma }^{+}$ and the probe has ${\sigma }^{-}$ polarization. An interpretation in terms of competition between two trap states and a dressed-atom model is presented. The observed extreme sensitivity of the resonance frequency to the external magnetic field is attributed to the “scissors effect” of the dressed states’ crossing point.