Inhibition of electromagnetically induced absorption due to excited-state decoherence in Rb vapor

The explanation presented by Taichenachev et al. [Phys. Rev. A $61,$ 011802 (2000)] according to which the electromagnetically induced absorption (EIA) resonances observed in degenerate two-level systems are due to coherence transfer from the excited to the ground state is experimentally tested in a Hanle-type experiment observing the parametric resonance on the $D1\mathrm{}$ line of ${}^{87}\mathrm{Rb}.$ While EIA occurs in the $F=\overrightarrow{1}{F}^{\prime }=2\mathrm{}$ transition in a cell containing only Rb vapor, collisions with a buffer gas (30 torr of Ne) cause the sign reversal of this resonance as a consequence of collisional decoherence of the excited state. A theoretical model in good qualitative agreement with the experimental results is presented.