Wall-induced Ramsey effects on electromagnetically induced absorption.

The effect of wall-induced Ramsey interference on the electromagnetically induced absorption (EIA) in an anti-relaxation coated vapor cell is studied in a four-level closed N-type atomic system. We show that the atomic coherence spontaneously transferred from the excited states to the ground states may interfere via the Ramsey sequence of the moving atoms with decoherence-free wall collisions. The spectral narrowing of the EIA resonance lineshape is induced by the Ramsey effect because of the long lifetime of the spontaneously transferred atomic coherence between the ground states. This calculated Ramsey EIA spectrum is in good agreement with the narrow EIA spectrum obtained experimentally in the anti-relaxation coated vapor cell.