Sub-hertz optical transitions in excited Yb$^+$

Abstract

We present the observation of three semi-forbidden transitions in singly-ionized ytterbium from the metastable $^{2}\mathrm{F}^o_{7/2}$ state. Owing to the long lifetimes of both the upper and lower states involved, these transitions are narrow and complement those already frequently used in this atom for quantum information and searches for new physics. We report the absolute frequencies of these electric quadrupole transitions, their isotope shifts, hyperfine structure, and measurements of the quadrupole transition moments. We find that the spontaneous lifetimes of these excited states are limited by slow magnetic dipole emission to lower-lying, odd-parity states, the lowest of which is accessible by laser excitation from ${}^2\mathrm{F}_{7/2}^o$ and is an attractive candidate for hosting a long-lived qubit.

Figures (6)

• Figure 1: Level diagram displaying driven transitions from the $^{2}\mathrm{F}^o_{7/2}$ state in $\mathrm{Yb^+}$.
• Figure 2: $^2\mathrm{F}_{7/2}^o \leftrightarrow {}^3[7/2]_{9/2}^o$, $|\Delta m_J|=1$ transition spectra across all stable even isotopes of Yb$^+$. The population distribution across the Zeeman sublevels of the $^2\mathrm{F}_{7/2}^o$ state results in the asymmetry between the $\Delta m_J=-1$ (lower frequency) feature and $\Delta m_J=+1$ (higher frequency) feature in each isotope. The linewidth of our spectroscopy laser is represented by the scale bar in the ${}^{170}\mathrm{Yb}^+$ subplot.
• Figure 3: King plot comparing the modified isotope shifts of the driven transitions against those of the $^{2}\mathrm{S}_{1/2} \leftrightarrow \, ^{2}\mathrm{D}_{5/2}$ measured by the Vuletić group Hur_thesis. Note that only the $^{2}\mathrm{F}^{o}_{7/2} \leftrightarrow \, ^{3}[7/2]^{o}_{9/2}$ transition was measured for $^{168} \mathrm{Yb}^+.$
• Figure 4: Hyperfine structure of $^{171}\mathrm{Yb}^+$ of the excited state and the $^{2}\mathrm{F}_{7/2}^o$. The centroid frequency of each transition is presented along with the hyperfine splitting of each excited state.
• Figure 5: $M1$ decay pathways from ${}^3[7/2]^o_{9/2}$, ${}^1[11/2]^o_{11/2}$, and ${}^3[9/2]^o_{9/2}$. The presented $M1$ lifetimes and branching ratios are theoretically calculated. The energy levels are sourced from NIST_ASD.