Control of spontaneous emission from a coherently driven four-level atom

Abstract

We study the spontaneous-emission properties of a coherently driven four-level atom, and show a few interesting phenomena such as fluorescence quenching, spectral-line narrowing, spectral-line enhancement, and spectral-line elimination. These phenomena can be observed in experiment since the rigorous condition of near-degenerate levels with nonorthogonal dipole moments is not required here. Qualitatively, these phenomena can be attributed to the quantum interference between competitive spontaneous-decay channels in the bare-state picture or the spontaneously generated coherence between two close-lying levels in the dressed-state picture.