Physical Review A

Collisional population transfer in trapped Yb+ ions

Martin M. Schauer, James R. Danielson, Angela-Maithy N. Nguyen, Li-Bang Wang, Xinxin Zhao, Justin R. Torgerson

Published Jun 5, 2009• 13 citations

Abstract

Long-lived metastable states of ${\text{Yb}}^{+}$ 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 ${\text{Yb}}^{+}$ ions into the long-lived ${^{2}F}_{7/2}$ state by means of collisions between He buffer gas and ${\text{Yb}}^{+}$ 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.

DOI: 10.1103/physreva.79.062705

Related papers

Thermal atom-ion collisions in a K- Yb+ hybrid system

Thai M. Hoang, Peter D. D. Schwindt, Yuan‐Yu Jau

arXiv:1901.00905Physical Review AAug 1, 20192 citations

A metastable state in $\mathrm{Yb}^+$ with lifetime greater than 10 minutes

Hassan Farhat, William Liu, Wesley C. Campbell

arXiv:2609.09523Sep 8, 20260 citations

Observation of collisions between cold Li atoms and Yb+ ions

J. Joger, Henning A. Fürst, Norman Vincenz Ewald +3 more

arXiv:1707.01729Physical Review ASep 25, 201765 citations

Production of YbH+ by chemical reaction of Yb+ in excited states with H2 gas

Kazuhiko Sugiyama, Jun Yoda

Physical Review AJan 1, 1997291 citations

Efficient quenching of population trapping in excited Yb+

David J. Seidel, Lute Maleki

Physical Review AApr 1, 199513 citations

Population trapping in excited Yb ions

H. Lehmitz, J. Hattendorf-Ledwoch, R. Blatt +1 more

Physical Review LettersMay 1, 198972 citations

Physical Review A

Collisional population transfer in trapped Yb+ ions

Martin M. Schauer, James R. Danielson, Angela-Maithy N. Nguyen, Li-Bang Wang, Xinxin Zhao, Justin R. Torgerson

Published Jun 5, 2009• 13 citations

Publisher

Abstract

Long-lived metastable states of

{\text{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

{\text{Yb}}^{+}

ions into the long-lived

{^{2}F}_{7/2}

state by means of collisions between He buffer gas and

{\text{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.

DOI: 10.1103/physreva.79.062705

Related papers

Thermal atom-ion collisions in a K- Yb+ hybrid system

Thai M. Hoang, Peter D. D. Schwindt, Yuan‐Yu Jau

We present experimental studies of atom-ion collisions using buffer-gas cooled, trapped ytterbium ( ${\mathrm{Yb}}^{+}$ ) ions immersed in potassium (K) vapor. The range of the collisional temperature is on the order of several hundred kelvin (thermal regime). We have determined various collisional rate coefficients of the ${\mathrm{Yb}}^{+}$ ion per K-atom number density. We find the upper bounds of charge-exchange rate coefficients ${\ensuremath{\kappa}}_{\mathrm{ce}}$ to be $(12.7\ifmmode\pm\else\textpm\fi{}1.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$ for K- $^{171}\mathrm{Yb}^{+}$ and $(5.3\ifmmode\pm\else\textpm\fi{}0.7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$ for K- $^{172}\mathrm{Yb}^{+}$ . For both isotopes, the spin-destruction rate coefficient ${\ensuremath{\kappa}}_{\mathrm{sd}}$ has an upper bound at $(1.46\ifmmode\pm\else\textpm\fi{}0.77)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$. The spin-exchange rate coefficient ${\ensuremath{\kappa}}_{\mathrm{se}}$ is measured to be $(1.64\ifmmode\pm\else\textpm\fi{}0.51)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$. The relatively low charge-exchange rate reported here demonstrates the advantage of using K atoms to sympathetically cool ${\mathrm{Yb}}^{+}$ ions and the relatively high spin-exchange rate may benefit research work in quantum metrology and quantum information processing on an atom-ion platform using K atoms and ${\mathrm{Yb}}^{+}$ ions.We present experimental studies of atom-ion collisions using buffer-gas cooled, trapped ytterbium (${\mathrm{Yb}}^{+}$) ions immersed in potassium (K) vapor. The range of the collisional temperature is on the order of several hundred kelvin (thermal regime). We have determined various collisional rate coefficients of the ${\mathrm{Yb}}^{+}$ ion per K-atom number density. We find the upper bounds of charge-exchange rate coefficients ${\ensuremath{\kappa}}_{\mathrm{ce}}$ to be $(12.7\ifmmode\pm\else\textpm\fi{}1.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$ for K-$^{171}\mathrm{Yb}^{+}$ and $(5.3\ifmmode\pm\else\textpm\fi{}0.7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$ for K-$^{172}\mathrm{Yb}^{+}$. For both isotopes, the spin-destruction rate coefficient ${\ensuremath{\kappa}}_{\mathrm{sd}}$ has an upper bound at $(1.46\ifmmode\pm\else\textpm\fi{}0.77)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$. The spin-exchange rate coefficient ${\ensuremath{\kappa}}_{\mathrm{se}}$ is measured to be $(1.64\ifmmode\pm\else\textpm\fi{}0.51)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$. The relatively low charge-exchange rate reported here demonstrates the advantage of using K atoms to sympathetically cool ${\mathrm{Yb}}^{+}$ ions and the relatively high spin-exchange rate may benefit research work in quantum metrology and quantum information processing on an atom-ion platform using K atoms and ${\mathrm{Yb}}^{+}$ ions.

arXiv:1901.00905Physical Review AAug 1, 20192 citations

A metastable state in $\mathrm{Yb}^+$ with lifetime greater than 10 minutesA metastable state in $\mathrm{Yb}^+$ with lifetime greater than 10 minutes

Hassan Farhat, William Liu, Wesley C. Campbell

We find through direct, time-domain measurement of trapped $\mathrm{Yb}^+$ ions that the excited ${}^3[11/2]_{9/2}^o$ state has a collision-free lifetime of 17.8(6) min, long enough for use in atomic clockwork or quantum information processing. We locate and benchmark a broad ``repump'' transition at $701\, \mathrm{nm}$ that readily transfers population back into the Doppler cooling cycle with the ground state, which may allow for quantum nondemolition measurement of sub-structure in the metastable manifold. Using a bi-stable Coulomb-crystal manometer, we find that the collisional quenching of this metastable ${}^3[11/2]_{9/2}^o$ manifold by background gas is more efficient than for ${}^2\mathrm{F}_{7/2}^o$ , but nonetheless we observe an average lifetime exceeding 10 minutes at the base pressure of our apparatus.We find through direct, time-domain measurement of trapped $\mathrm{Yb}^+$ ions that the excited ${}^3[11/2]_{9/2}^o$ state has a collision-free lifetime of 17.8(6) min, long enough for use in atomic clockwork or quantum information processing. We locate and benchmark a broad ``repump'' transition at $701\, \mathrm{nm}$ that readily transfers population back into the Doppler cooling cycle with the ground state, which may allow for quantum nondemolition measurement of sub-structure in the metastable manifold. Using a bi-stable Coulomb-crystal manometer, we find that the collisional quenching of this metastable ${}^3[11/2]_{9/2}^o$ manifold by background gas is more efficient than for ${}^2\mathrm{F}_{7/2}^o$, but nonetheless we observe an average lifetime exceeding 10 minutes at the base pressure of our apparatus.

arXiv:2609.09523Sep 8, 20260 citations

Observation of collisions between cold Li atoms and Yb+ ions

J. Joger, Henning A. Fürst, Norman Vincenz Ewald +3 more

We report on the observation of cold collisions between $^{6}\mathrm{Li}$ atoms and ${\mathrm{Yb}}^{+}$ ions. This combination of species has recently been proposed as the most suitable for reaching the quantum limit in hybrid atom-ion systems, due to its large mass ratio. For atoms and ions prepared in the $^{2}S_{1/2}$ ground state, the charge-transfer and association rate is found to be at least ${10}^{3}$ times smaller than the Langevin collision rate. These results confirm the excellent prospects of $^{6}\mathrm{Li}\ensuremath{-}{\mathrm{Yb}}^{+}$ for sympathetic cooling and quantum information applications. For ions prepared in the excited electronic states $^{2}P_{1/2}, ^{2}D_{3/2}$ , and $^{2}F_{7/2}$ , we find that the reaction rate is dominated by charge transfer and does not depend on the ionic isotope or the collision energy in the range $\ensuremath{\sim}1--120\phantom{\rule{0.16em}{0ex}}\mathrm{mK}$. The low charge-transfer rate for ground-state collisions is corroborated by theory, but the $4f$ shell in the ${\mathrm{Yb}}^{+}$ ion prevents an accurate prediction for the charge-transfer rate of the $^{2}P_{1/2}, ^{2}D_{3/2}$ , and $^{2}F_{7/2}$ states. Using ab initio methods of quantum chemistry we calculate the atom-ion interaction potentials up to energies of $30\ifmmode\times\else\texttimes\fi{}{10}^{3}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, and use these to give qualitative explanations of the observed rates.We report on the observation of cold collisions between $^{6}\mathrm{Li}$ atoms and ${\mathrm{Yb}}^{+}$ ions. This combination of species has recently been proposed as the most suitable for reaching the quantum limit in hybrid atom-ion systems, due to its large mass ratio. For atoms and ions prepared in the $^{2}S_{1/2}$ ground state, the charge-transfer and association rate is found to be at least ${10}^{3}$ times smaller than the Langevin collision rate. These results confirm the excellent prospects of $^{6}\mathrm{Li}\ensuremath{-}{\mathrm{Yb}}^{+}$ for sympathetic cooling and quantum information applications. For ions prepared in the excited electronic states $^{2}P_{1/2}, ^{2}D_{3/2}$, and $^{2}F_{7/2}$, we find that the reaction rate is dominated by charge transfer and does not depend on the ionic isotope or the collision energy in the range $\ensuremath{\sim}1--120\phantom{\rule{0.16em}{0ex}}\mathrm{mK}$. The low charge-transfer rate for ground-state collisions is corroborated by theory, but the $4f$ shell in the ${\mathrm{Yb}}^{+}$ ion prevents an accurate prediction for the charge-transfer rate of the $^{2}P_{1/2}, ^{2}D_{3/2}$, and $^{2}F_{7/2}$ states. Using ab initio methods of quantum chemistry we calculate the atom-ion interaction potentials up to energies of $30\ifmmode\times\else\texttimes\fi{}{10}^{3}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, and use these to give qualitative explanations of the observed rates.

arXiv:1707.01729Physical Review ASep 25, 201765 citations

Production of YbH+ by chemical reaction of Yb+ in excited states with H2 gas

Kazuhiko Sugiyama, Jun Yoda

It is known that fluorescence of trapped ${\mathrm{Yb}}^{+}$ ions fades with continuous driving of the $^{2}$ ${\mathrm{S}}_{1\mathrm{/}2}$ ${\mathrm{\ensuremath{-}}}^{2}$ ${\mathrm{P}}_{1\mathrm{/}2}$ transition in the presence of buffer gases. This phenomenon has been interpreted as being caused by population trapping in the $^{2}$ ${\mathrm{F}}_{7\mathrm{/}2}$ state of ${\mathrm{Yb}}^{+}$ . As another cause of the fluorescence disappearance, we found the production of ${\mathrm{YbH}}^{+}$ by chemical reaction of ${\mathrm{Yb}}^{+}$ in excited states with ${\mathrm{H}}_{2}$ gas. We found that the wavelengths of 369.482, 369.202, and 368.947 nm, formerly assigned as wavelengths for deexcitation of ${\mathrm{Yb}}^{+}$ in the $^{2}$ ${\mathrm{F}}_{7\mathrm{/}2}$ state to the $^{2}$ ${\mathrm{S}}_{1\mathrm{/}2}$ ground state, are actually photodissociation lines of ${\mathrm{YbH}}^{+}$ . The change of the resonance point of rf resonance absorption signals indicates the production and dissociation of ${\mathrm{YbH}}^{+}$ ions. The production of ${\mathrm{YbH}}^{+}$ may be a problem in establishing frequency standards using buffer-gas-cooled ${\mathrm{Yb}}^{+}$ , owing to difficulty in removing ${\mathrm{H}}_{2}$ gas from vacuum systems.It is known that fluorescence of trapped ${\mathrm{Yb}}^{+}$ ions fades with continuous driving of the $^{2}$ ${\mathrm{S}}_{1\mathrm{/}2}$${\mathrm{\ensuremath{-}}}^{2}$${\mathrm{P}}_{1\mathrm{/}2}$ transition in the presence of buffer gases. This phenomenon has been interpreted as being caused by population trapping in the $^{2}$ ${\mathrm{F}}_{7\mathrm{/}2}$ state of ${\mathrm{Yb}}^{+}$ . As another cause of the fluorescence disappearance, we found the production of ${\mathrm{YbH}}^{+}$ by chemical reaction of ${\mathrm{Yb}}^{+}$ in excited states with ${\mathrm{H}}_{2}$ gas. We found that the wavelengths of 369.482, 369.202, and 368.947 nm, formerly assigned as wavelengths for deexcitation of ${\mathrm{Yb}}^{+}$ in the $^{2}$ ${\mathrm{F}}_{7\mathrm{/}2}$ state to the $^{2}$ ${\mathrm{S}}_{1\mathrm{/}2}$ ground state, are actually photodissociation lines of ${\mathrm{YbH}}^{+}$ . The change of the resonance point of rf resonance absorption signals indicates the production and dissociation of ${\mathrm{YbH}}^{+}$ ions. The production of ${\mathrm{YbH}}^{+}$ may be a problem in establishing frequency standards using buffer-gas-cooled ${\mathrm{Yb}}^{+}$ , owing to difficulty in removing ${\mathrm{H}}_{2}$ gas from vacuum systems.

Physical Review AJan 1, 1997291 citations

Efficient quenching of population trapping in excited Yb+

David J. Seidel, Lute Maleki

We report on a study to determine the efficiency of various buffer gases in quenching the population trapping states of laser-excited ytterbium ions. The ions were confined in an rf-dc hybrid trap, and their $^{2}$ ${\mathit{S}}_{1/2}$ ${\mathrm{\ensuremath{\leftrightarrows}}}^{2}$ ${\mathit{P}}_{3/2}$ transition was excited with 329-nm laser light. Buffer gases used include ${\mathrm{H}}_{2}$ , ${\mathrm{N}}_{2}$ , ${\mathrm{CO}}_{2}$ , Ar, and He at several different pressure regimes. We have identified ${\mathrm{N}}_{2}$ to be highly efficient in quenching the population of the trapping states and thus be the most suitable buffer gas to use with ytterbium for the development of a trapped-ion microwave frequency standard.We report on a study to determine the efficiency of various buffer gases in quenching the population trapping states of laser-excited ytterbium ions. The ions were confined in an rf-dc hybrid trap, and their $^{2}$${\mathit{S}}_{1/2}$${\mathrm{\ensuremath{\leftrightarrows}}}^{2}$${\mathit{P}}_{3/2}$ transition was excited with 329-nm laser light. Buffer gases used include ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, ${\mathrm{CO}}_{2}$, Ar, and He at several different pressure regimes. We have identified ${\mathrm{N}}_{2}$ to be highly efficient in quenching the population of the trapping states and thus be the most suitable buffer gas to use with ytterbium for the development of a trapped-ion microwave frequency standard.

Physical Review AApr 1, 199513 citations

Population trapping in excited Yb ions

H. Lehmitz, J. Hattendorf-Ledwoch, R. Blatt +1 more

Resonant laser excitation of Yb ions confined in an rf ion trap is found to result in perfect population trapping in the highly metastable $^{2}\mathrm{F}_{7/2}$ 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.Resonant laser excitation of Yb ions confined in an rf ion trap is found to result in perfect population trapping in the highly metastable $^{2}\mathrm{F}_{7/2}$ 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.

Physical Review LettersMay 1, 198972 citations

Long-lived metastable states of

{\text{Yb}}^{+}

{\text{Yb}}^{+}

ions into the long-lived

{^{2}F}_{7/2}

state by means of collisions between He buffer gas and

{\text{Yb}}^{+}

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.

We present experimental studies of atom-ion collisions using buffer-gas cooled, trapped ytterbium (

{\mathrm{Yb}}^{+}

) ions immersed in potassium (K) vapor. The range of the collisional temperature is on the order of several hundred kelvin (thermal regime). We have determined various collisional rate coefficients of the

{\mathrm{Yb}}^{+}

ion per K-atom number density. We find the upper bounds of charge-exchange rate coefficients ${\ensuremath{\kappa}}_{\mathrm{ce}}$ to be $(12.7\ifmmode\pm\else\textpm\fi{}1.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$ for K-

^{171}\mathrm{Yb}^{+}

and $(5.3\ifmmode\pm\else\textpm\fi{}0.7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$ for K-

^{172}\mathrm{Yb}^{+}

. For both isotopes, the spin-destruction rate coefficient ${\ensuremath{\kappa}}_{\mathrm{sd}}$ has an upper bound at $(1.46\ifmmode\pm\else\textpm\fi{}0.77)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$. The spin-exchange rate coefficient ${\ensuremath{\kappa}}_{\mathrm{se}}$ is measured to be $(1.64\ifmmode\pm\else\textpm\fi{}0.51)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$. The relatively low charge-exchange rate reported here demonstrates the advantage of using K atoms to sympathetically cool

{\mathrm{Yb}}^{+}

ions and the relatively high spin-exchange rate may benefit research work in quantum metrology and quantum information processing on an atom-ion platform using K atoms and

{\mathrm{Yb}}^{+}

ions.

A metastable state in

\mathrm{Yb}^+

with lifetime greater than 10 minutes

We find through direct, time-domain measurement of trapped

\mathrm{Yb}^+

ions that the excited

{}^3[11/2]_{9/2}^o

state has a collision-free lifetime of 17.8(6) min, long enough for use in atomic clockwork or quantum information processing. We locate and benchmark a broad ``repump'' transition at

701\, \mathrm{nm}

that readily transfers population back into the Doppler cooling cycle with the ground state, which may allow for quantum nondemolition measurement of sub-structure in the metastable manifold. Using a bi-stable Coulomb-crystal manometer, we find that the collisional quenching of this metastable

{}^3[11/2]_{9/2}^o

manifold by background gas is more efficient than for

{}^2\mathrm{F}_{7/2}^o

, but nonetheless we observe an average lifetime exceeding 10 minutes at the base pressure of our apparatus.

We report on the observation of cold collisions between

^{6}\mathrm{Li}

atoms and

{\mathrm{Yb}}^{+}

ions. This combination of species has recently been proposed as the most suitable for reaching the quantum limit in hybrid atom-ion systems, due to its large mass ratio. For atoms and ions prepared in the

^{2}S_{1/2}

ground state, the charge-transfer and association rate is found to be at least

{10}^{3}

times smaller than the Langevin collision rate. These results confirm the excellent prospects of $^{6}\mathrm{Li}\ensuremath{-}{\mathrm{Yb}}^{+}$ for sympathetic cooling and quantum information applications. For ions prepared in the excited electronic states

^{2}P_{1/2}, ^{2}D_{3/2}

, and

^{2}F_{7/2}

, we find that the reaction rate is dominated by charge transfer and does not depend on the ionic isotope or the collision energy in the range $\ensuremath{\sim}1--120\phantom{\rule{0.16em}{0ex}}\mathrm{mK}$. The low charge-transfer rate for ground-state collisions is corroborated by theory, but the

4f

shell in the

{\mathrm{Yb}}^{+}

ion prevents an accurate prediction for the charge-transfer rate of the

^{2}P_{1/2}, ^{2}D_{3/2}

, and

^{2}F_{7/2}

states. Using ab initio methods of quantum chemistry we calculate the atom-ion interaction potentials up to energies of $30\ifmmode\times\else\texttimes\fi{}{10}^{3}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, and use these to give qualitative explanations of the observed rates.

It is known that fluorescence of trapped

{\mathrm{Yb}}^{+}

ions fades with continuous driving of the

^{2}

{\mathrm{S}}_{1\mathrm{/}2}

${\mathrm{\ensuremath{-}}}^{2}$

{\mathrm{P}}_{1\mathrm{/}2}

transition in the presence of buffer gases. This phenomenon has been interpreted as being caused by population trapping in the

^{2}

{\mathrm{F}}_{7\mathrm{/}2}

state of

{\mathrm{Yb}}^{+}

. As another cause of the fluorescence disappearance, we found the production of

{\mathrm{YbH}}^{+}

by chemical reaction of

{\mathrm{Yb}}^{+}

in excited states with

{\mathrm{H}}_{2}

gas. We found that the wavelengths of 369.482, 369.202, and 368.947 nm, formerly assigned as wavelengths for deexcitation of

{\mathrm{Yb}}^{+}

in the

^{2}

{\mathrm{F}}_{7\mathrm{/}2}

state to the

^{2}

{\mathrm{S}}_{1\mathrm{/}2}

ground state, are actually photodissociation lines of

{\mathrm{YbH}}^{+}

. The change of the resonance point of rf resonance absorption signals indicates the production and dissociation of

{\mathrm{YbH}}^{+}

ions. The production of

{\mathrm{YbH}}^{+}

may be a problem in establishing frequency standards using buffer-gas-cooled

{\mathrm{Yb}}^{+}

, owing to difficulty in removing

{\mathrm{H}}_{2}

gas from vacuum systems.

^{2}

{\mathit{S}}_{1/2}

${\mathrm{\ensuremath{\leftrightarrows}}}^{2}$

{\mathit{P}}_{3/2}

transition was excited with 329-nm laser light. Buffer gases used include

{\mathrm{H}}_{2}

{\mathrm{N}}_{2}

{\mathrm{CO}}_{2}

, Ar, and He at several different pressure regimes. We have identified

{\mathrm{N}}_{2}

to be highly efficient in quenching the population of the trapping states and thus be the most suitable buffer gas to use with ytterbium for the development of a trapped-ion microwave frequency standard.

Resonant laser excitation of Yb ions confined in an rf ion trap is found to result in perfect population trapping in the highly metastable

^{2}\mathrm{F}_{7/2}

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.