Long-lived metastable states in the 4f$^{13}$5d6s configuration of Yb$^+$

Abstract

We study the occurrence of long-lived metastable states in the 4f$^{13}$5d6s electron configuration of Yb$^+$. By optical pumping of a single trapped ion on the $^2F^\text{o}_{7/2}\rightarrow (7/2,0)_{7/2}$ transition at 377.5 nm, we prepare a wide range of metastable electronic states. We use a co-trapped control ion to sympathetically cool the spectroscopy ion, allowing us to accurately time its subsequent decay. We record a strong decay signal corresponding to a lifetime of 0.92(8) s, a weaker decay signal with lifetime 9.8(+2.9, -2.0) s, and find evidence for a much longer lifetime, $>$ 30 s. We identify the metastable states with these lifetimes qualitatively, and corroborate our results with atomic structure calculations that support the observed lifetimes and decay paths. These long-lived states provide new opportunities in qubit and qudit state detection and optical clocks.

Figures (5)

• Figure 1: Experimental sequence and level scheme. (a) Both ions are prepared in the $^2F^\text{o}_{7/2}$ state using a 411 nm laser pulse driving the $^2S_{1/2}\rightarrow\,^2D_{5/2}$ transition followed by decay to $^2F^\text{o}_{7/2}$. (b) The spectroscopy ion is driven on the 377.5 nm $^2F^\text{o}_{7/2}\rightarrow (7/2,0)_{7/2}$ transition, followed by possible decay to metastable states. (c) The control ion is returned to the ground state via the 760 nm $^2F^\text{o}_{7/2}\rightarrow {}^1[3/2]^\text{o}_{3/2}$ transition. (d) Fluorescence detection with lasers at 370 nm and 935 nm to observe at what time the spectroscopy ion decays back to a state belonging to the fluorescence cycle ($^2S_{1/2}$ and $^2D_{3/2}$). We can perform this last step with or without the 760 nm laser, allowing us to distinguish decay paths including or excluding decay to the $^2F^\text{o}_{7/2}$ state. The control ion keeps the spectroscopy ion cold while it is in a metastable state, such that we can accurately determine its return time.
• Figure 2: Measured cumulative probability that the spectroscopy ion is dark as a function of the wait time, for different experimental sequence configurations. (■) The 760 nm laser on during the wait time. (●) The 760 nm laser off during the wait time. (■) Control measurement in which the 377.5 nm pulse is omitted with the 760 nm laser on. (●) Control measurement with the 760 nm laser off. The blue (red) curve represents the function $C(t)=1-\alpha P(t)+\beta$, as explained in the text, fitted to the data with the 760 nm laser on(off) during the wait time.
• Figure 3: Partial level scheme of Yb$^+$ showing the laser driving the $^2F^\text{o}_{7/2}\rightarrow (7/2,0)_{7/2}$ transition (thick blue arrow). We include the dominant E1 decay channels observed in discharge experiments Meggers:1967 as well as the weaker configuration interaction-induced (CI) E1 decay channels of the metatsable states, M1 decay and E2 decay. To improve clarity we only indicate expected dominant decay channels for the metastable states of interest. Data taken from the NIST database NIST_DATABASE.
• Figure 4: (a) Laser configuration for spectroscopy. (b) Ion fluorescence as a function of 377.4 nm beam position.
• Figure 5: Measured cumulative probability that the spectroscopy ion is dark as a function of the wait time, for different experimental sequence configurations. (■) The 760 nm laser on during the wait time. (●) The 760 nm laser off during the wait time. (■) Control measurement in which the 377.5 nm pulse is omitted with the 760 nm laser on. (●) Control measurement with the 760 nm laser off. The blue(red) curve represents the function $C(t)=1-\alpha P(t)+\beta$, as explained in the text, fitted to the data with the 760 nm laser on (off) during the wait time. Compared to the laser powers used in the original measurement, (a) the 370 nm power is increased by a factor $\sim$ 2.8 and (b) the 370 nm power is increased by a factor $\sim$ 1.4 and the 935 nm power is halved.