Strong fields, resonances, and spontaneous transitions in atoms. Interference in multiphoton transitions and resonance fluorescence

Fuli Li, Shi‐Yao Zhu, Ma Ai-Qun

The interaction of a four-level atom consisting of one excited state, two upper levels and one ground state is considered. We use one field to drive the transition between the excited state and the ground state, and simultaneously apply another field to couple two transitions from the upper-level doublet to the ground state. We investigate how to control the central linewidth of resonance fluorescence spectrum of the driven transition via quantum interference between two transitions from the upper doublet to the ground state of the atom. In the case of orthogonal dipole moments for the upper doublet and the ground state the widths of the central line and the sidebands of the resonance fluorescence spectrum are totally controlled by the spontaneous emission rate of the upper doublet when the applying field is sufficiently strong. When the dipole moments are parallel, the central linewidth can be much narrower than the linewidths of spontaneous emission of the excited state and of the upper doublet due to the quantum interference. The smaller the upper doublet splitting, the narrower the central linewidth. We also notice that when the upper levels are degenerate the resonance fluorescence spectrum may depend on the initial condition because of the quantum interference.

I. V. Lebedev

Philip George Burke

Fei Wang, Wen-Xing Shi, Cheng Gong

In this paper, we investigate the spontaneously generated coherence (SGC) effects on the fluorescence fields intensity-intensity correlation in a resonant driven four-level Y-type atomic system. By using a strong control field, in the absense of SGC effects, strong correlation and anticorrelation fluorescence photons can be produced from two ladder transitions in this system respectively. However, in the presence of SGC effects, the fluorescence fields correlation properties are reversed for the two transitions. The above phenomena can be traced to the quantum destructive or constructive interference in terms of dressed states.

I. V. Lebedev

M. A. G. Martinez, Peter R. Herczfeld, Charles Samuels +2 more

We discuss quantum interference effects in the resonance fluorescence spectrum of a \ensuremath{\Lambda} three-level atom when the lower-level doublet is driven by a coherent field. The interfering pathways that lead to the same final state involve both spontaneous decays and stimulated transitions, and differ from one another by an odd number of stimulated processes induced by the driving field. As a consequence, the interference structures depend upon the phase of the coherent field, an effect that is absent in other resonance fluorescence phenomena. The phase dependence of the quantum interference contribution is especially significant when the level splitting of the driven doublet is comparable to the spontaneous decay rates of the competing optical paths.