Trapping of Neutral Mercury Atoms and Prospects for Optical Lattice Clocks

We report vapor-cell magneto-optical trapping of Hg isotopes on the ${}^{1}S_0\mathrm{\text{−}}{}^{3}P_1$ intercombination transition. Six abundant isotopes, including four bosons and two fermions, were trapped. Hg is the heaviest nonradioactive atom trapped so far, which enables sensitive atomic searches for “new physics” beyond the standard model. We propose an accurate optical lattice clock based on Hg and evaluate its systematic accuracy to be better than ${10}^{-18}$. Highly accurate and stable Hg-based clocks will provide a new avenue for the research of optical lattice clocks and the time variation of the fine-structure constant.

Figure 1

Energy-level diagram for Hg. The ${}^{1}S_0\mathrm{\text{−}}{}^{3}P_1$ transition at 253.7 nm is used for magneto-optical trapping of the atoms. The ${}^{1}S_0\mathrm{\text{−}}{}^{3}P_0$ transition at 265.6 nm serves as a clock oscillator. The “magic wavelength,” ${\lambda }_L=360\mathrm{nm}$, is the far-off resonance for the relevant transitions originating from the ${}^{1}S_0$ and ${}^{3}P_0$ levels.

Figure 2

Experimental setup. A 253.7 nm UV light was generated by frequency quadrupling a diode laser operated at 1014.9 nm with nearly 1 W. A 10 mW UV light was fed into a vacuum chamber to form a vapor-cell MOT with a folded beam configuration. ECLD, external-cavity laser diode; OI, optical isolator; TA, tapered amplifier; PZT: piezoelectric transducer, QWP: quarter wave plate.

Figure 3

Fluorescence spectrum of magneto-optically trapped Hg isotopes as a function of the laser frequency at 253.7 nm. The bars at the bottom indicate the positions of the resonances of individual isotopes. Detailed profiles are drawn using the magnified frequency scale shown at the top.