Laser Cooling to the Zero-Point Energy of Motion

A single trapped ${}_{}{}^{198}{}_{}{}^{}\mathrm{Hg}_{}^{+}{}_{}{}^{}$ ion was cooled by scattering laser radiation that was tuned to the resolved lower motional sideband of the narrow ${}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}-{}_{}{}^2{}_{}{}^{}D_{\frac{5}{2}}^{}{}_{}{}^{}$ transition. The different absorption strengths on the upper and lower sidebands after cooling indicated that the ion was in the ground state of its confining well approximately 95% of the time.