Resonance fluorescence spectrum of a trapped ion undergoing quantum jumps

We experimentally investigate the resonance fluorescence spectrum of single ¹⁷¹Yb and ¹⁷²Yb ions that are laser cooled to the Lamb-Dicke regime in a radiofrequency trap. While the fluorescence scattering of ¹⁷²Yb is continuous, the ¹⁷¹Yb fluorescence is interrupted by quantum jumps because a nonvanishing rate of spontaneous transitions leads to electron shelving in the metastable hyperfine sublevel ²D_3/2(F=2). The average duration of the resulting dark periods can be varied by changing the intensity of a repumping laser field. Optical heterodyne detection is employed to analyze the fluorescence spectrum near the Rayleigh elastic scattering peak. It is found that the stochastic modulation of the fluorescence emission by quantum jumps gives rise to a Lorentzian component in the fluorescence spectrum, and that the linewidth of this component varies according to the average duration of the dark fluorescence periods. The experimental observations are in quantitative agreement with theoretical predictions.