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

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.

Figure 1

Schematic diagram of a coherently driven four-level atom, which consists of (a) an upper level and three lower levels in the bare-state picture, and (b) two upper levels and two lower levels in the dressed-state picture of one driving field.

Figure 2

Spontaneous-emission spectra $S\left({\delta }_k\right)$ (in arbitary units) for (a) ${\Delta }_p=0.2\gamma$ and ${\Delta }_c=0.0$; (b) ${\Delta }_p=1.0\gamma$ and ${\Delta }_c=-1.2\gamma$. Other parameters are ${\Omega }_c=0.5\gamma$, ${\Omega }_p=0.3\gamma$, ${\Gamma }_0=\gamma$, $a_0\left(0\right)=1.0$, $a_1\left(0\right)=0.0$, and $a_2\left(0\right)=0.0$.

Figure 3

Spontaneous-emission spectra $S\left({\delta }_k\right)$ (in arbitary units) for (a) ${\Delta }_p=0.2\gamma$ and ${\Delta }_c=0.0$; (b) ${\Delta }_p=1.0\gamma$ and ${\Delta }_c=-1.2\gamma$. Other parameters are ${\Omega }_c=0.5\gamma$, ${\Omega }_p=0.3\gamma$, ${\Gamma }_0=\gamma$, $a_0\left(0\right)=0.906$, $a_1\left(0\right)=0.3$, and $a_2\left(0\right)=0.3$.

Figure 4

Spontaneous-emission spectra $S\left({\delta }_k\right)$ (in arbitary units) for (a) $a_1\left(0\right)=1.0$ and $a_2\left(0\right)=0.0$; (b) $a_1\left(0\right)=0.707$ and $a_2\left(0\right)=0.707$. Other parameters are ${\Omega }_c=0.5\gamma$, ${\Omega }_p=0.3\gamma$, ${\Gamma }_0=\gamma$, ${\Delta }_p=0.1\gamma$, ${\Delta }_c=0.0$, and $a_0\left(0\right)=0.0$.

Figure 5

Spontaneous-emission spectra $S\left({\delta }_k\right)$ (in arbitary units) for (a) $a_0\left(0\right)=0.906$, $a_1\left(0\right)=0.3$, and $a_2\left(0\right)=0.3$; (b) $a_0\left(0\right)=0.0$, $a_1\left(0\right)=0.707$, and $a_2\left(0\right)=0.707$. Other parameters are ${\Omega }_c=0.5\gamma$, ${\Omega }_p=0.3\gamma$, ${\Gamma }_0=\gamma$, ${\Delta }_p=0.4\gamma$, and ${\Delta }_c=-0.3\gamma$.

Figure 6

Spontaneous-emission spectra $S\left({\delta }_k\right)$ (in arbitary units) for (a) ${\Delta }_p={\Delta }_c=0.0$; (b) ${\Delta }_p={\Delta }_c=0.2\gamma$. Other parameters are ${\Omega }_c=0.5\gamma$, ${\Omega }_p=0.3\gamma$, ${\Gamma }_0=\gamma$, $a_0\left(0\right)=0.0$, $a_1\left(0\right)=0.707$, and $a_2\left(0\right)=0.707$.