Long-lived metastable states of
Yb+ ions are used for atomic frequency standards, precision measurements, and quantum information research. The effect of population trapping and transfer in these states must be well understood. We report here the transfer of
Yb+ ions into the long-lived
2F7/2 state by means of collisions between He buffer gas and
Yb+ ions held in a linear Paul trap. Transfer rates were measured as functions of buffer-gas pressure and repump-laser power, and the collisional population transfer rates were extracted. The measured transfer rate coefficients are $8.32(75)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}$ and $8.65(33)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\text{ }{\text{cm}}^{3}/\text{s}$ for the collisional processes ${^{2}P}_{1/2}\ensuremath{\rightarrow}{^{2}D}_{5/2}$ and ${^{2}D}_{3/2}\ensuremath{\rightarrow}{^{2}F}_{7/2}$, respectively.
Resonant laser excitation of Yb ions confined in an rf ion trap is found to result in perfect population trapping in the highly metastable
2F7/2 state. The lifetime of this level is measured to be greater than 8 days. Population and depopulation of this level under narrow- and broad-band laser excitation conditions is investigated and its potentiality for ultimate-resolution laser spectroscopy indicated.
The metastable
32D3/2,5/2 doublet of
Ca+ ions stored in a Paul trap was investigated in the presence of different neutral gases, in the pressure range ${10}^{\mathrm{\ensuremath{-}}9}$--${10}^{\mathrm{\ensuremath{-}}6}$ mbar. The natural lifetimes were determined to be \ensuremath{\tau}(
D3/2)=1111\ifmmode\pm\else\textpm\fi{}46 ms and \ensuremath{\tau}(
D5/2)=994\ifmmode\pm\else\textpm\fi{}38 ms, which agree very well with previous experiments. The estimation of the quenching rates of
Ca+-He [${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{He}}$=(1.05\ifmmode\pm\else\textpm\fi{}0.42)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$
cm3 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$],
Ca+-Ne [${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{}\mathrm{Ne}}$=(0.9\ifmmode\pm\else\textpm\fi{}0.7)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$
cm3 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$], and
Ca+-
N2 [${\mathrm{\ensuremath{\Gamma}}}_{{\mathrm{N}}_{2}}$=(1.7\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$
cm3 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$] was carried out for collisions in the energy range 0.3--1.3 eV. In addition, rate constants for the mixing of the fine-structure states were measured in the presence of helium and nitrogen for the j=3/2\ensuremath{\rightarrow}j=5/2 case [${\ensuremath{\gamma}}_{35}$(He)=(2.24\ifmmode\pm\else\textpm\fi{}0.10)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$
cm3 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ and ${\ensuremath{\gamma}}_{35}$(
N2)=(2.8\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}9}$
cm3 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$] and for the j=5/2\ensuremath{\rightarrow}j=3/2 case [${\ensuremath{\gamma}}_{53}$(He)=(1.2\ifmmode\pm\else\textpm\fi{}0.7)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$
cm3 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ and ${\ensuremath{\gamma}}_{53}$(
N2)=(1.26\ifmmode\pm\else\textpm\fi{}0.10)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}9}$
cm3 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$]. The measurements were carried out populating the metastable levels by direct laser excitation of the forbidden S-D transitions.
We study the occurrence of long-lived metastable states in the 4f$^{13}
5d6selectronconfigurationofYb^+$. By optical pumping of a single trapped ion on the
2F7/2o→(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.
The suitability of the 411-nm ${}^{2}{S}_{1/2}{\ensuremath{-}}^{2}{D}_{5/2}$ transition in
Yb+ is assessed as an optical frequency standard. The lifetime of the
2D5/2 level has been measured and found to be 7.2\ifmmode\pm\else\textpm\fi{}0.3 ms, which implies a natural linewidth of 22.2\ifmmode\pm\else\textpm\fi{}0.9 Hz for the 411-nm transition. In addition to a decay to the ground state the
2D5/2 level can decay into the highly metastable
2F7/2 level where it is trapped. The branching ratio for decay into the
2F7/2 level has been measured and found to be 0.83\ifmmode\pm\else\textpm\fi{}0.03. A transition capable of rapidly depopulating the
2F7/2 level and returning the ion to the cooling cycle has been demonstrated. This has enabled a quantum jump measurement of the 411-nm transition in
172Yb+ to be performed, yielding a center frequency of 729 476 869.13(0.42) MHz (1\ensuremath{\sigma}).
A single
Ba+ atom was confined in a radio-frequency ion trap and cooled by near-resonant laser light. Quantum jumps into and out of the metastable 5d
2D5/2 level were observed that followed the expected exponential distribution in dark periods to good agreement. Measurement of quantum-jump distributions together with careful measurements of the absolute partial pressures of all residual gas species enabled accurate measurements of the quenched 5d
2D5/2 lifetime as a function of quenching gas pressure. Measurements of quenching were observed at pressures where the mean collision rate was on the order of 1 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. The results yielded quenching rate constants for the metastable level for a series of gases that typically make up the residual gas environment of ultra-high-vacuum systems (
H2, He,
CH4,
H2O, CO,
N2, Ar, and
CO2) together with an improved value of the
52D5/2 radiative lifetime of
t0=34.5\ifmmode\pm\else\textpm\fi{}3.5 s. The above quenching rate constants were then compared with classical ion-molecule collision theory. It was found that the quenching rates for molecular gases were comparable to the classical collision rates, while the rates for atomic gases were considerably lower.