Sub-dekahertz Ultraviolet Spectroscopy of199Hg+

Abstract

Using a laser that is frequency locked to a Fabry-P\'erot \'etalon of high finesse and stability, we probe the ${5d}^{10}6s^{2}S_{1/2}(F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0)\ensuremath{\leftrightarrow}{5d}^{9}{6s}^{2}^{2}D_{5/2}(F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2)$ $\ensuremath{\Delta}{m}_{F}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ electric-quadrupole transition of a single laser-cooled ${}^{199}{\mathrm{Hg}}^{+}$ ion stored in a cryogenic radio-frequency ion trap. We observe Fourier-transform limited linewidths as narrow as 6.7 Hz at 282 nm ( $1.06\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0ex}{0ex}}\mathrm{Hz}$), yielding a line $Q\ensuremath{\approx}1.6\ifmmode\times\else\texttimes\fi{}{10}^{14}$. We perform a preliminary measurement of the ${5d}^{9}{6s}^{2}^{2}D_{5/2}$ electric-quadrupole shift due to interaction with the static fields of the trap, and discuss the implications for future trapped-ion optical frequency standards.