Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2201.07330 · Physical Review Letters

Radium Ion Optical Clock

C. A. Holliman, Mingyu Fan, A. Contractor, Samuel M. Brewer, Andrew M. Jayich

Published Jan 20, 2022• 29 citations
arXivHTMLPDF

Abstract

We report the first operation of a ${\mathrm{Ra}}^{+}$ optical clock, a promising high-performance clock candidate. The clock uses a single trapped $^{226}{\mathrm{Ra}}^{+}$ ion and operates on the $7s\text{ }^{2}{S}_{1/2}\ensuremath{\rightarrow}6d\text{ }^{2}{D}_{5/2}$ electric quadrupole transition. By self-referencing three pairs of symmetric Zeeman transitions, we demonstrate a frequency instability of $1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}/\sqrt{\ensuremath{\tau}}$, where $\ensuremath{\tau}$ is the averaging time in seconds. The total systematic uncertainty is evaluated to be $\mathrm{\ensuremath{\Delta}}\ensuremath{\nu}/\ensuremath{\nu}=9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$. Using the clock, we realize the first measurement of the ratio of the ${D}_{5/2}$ state to the ${S}_{1/2}$ state Land\'e $g$-factors: ${g}_{D}/{g}_{S}=0.598\text{ }805\text{ }3(11)$. A ${\mathrm{Ra}}^{+}$ optical clock could improve limits on the time variation of the fine structure constant, $\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{\ensuremath{\alpha}}/\ensuremath{\alpha}$, in an optical frequency comparison. The ion also has several features that make it a suitable system for a transportable optical clock.

DOI
10.1103/physrevlett.128.033202

Related papers

Radium single-ion optical clock

Oscar O. Versolato, L. W. Wansbeek, Klaus Peter Jungmann +3 more

We explore the potential of the electric quadrupole transitions $7s\,^2S_{1/2}$ - $6d\,^2D_{3/2}$, $6d\,^2D_{5/2}$ in radium isotopes as single-ion optical frequency standards. The frequency shifts of the clock transitions due to external fields and the corresponding uncertainties are calculated. Several competitive $^A$Ra$^+$ candidates with $A=$ 223 - 229 are identified. In particular, we show that the transition $7s\,^2S_{1/2}\,(F=2,m_F=0)$ - $6d\,^2D_{3/2}\,(F=0,m_F=0)$ at 828 nm in $^{223}$Ra$^+$, with no linear Zeeman and electric quadrupole shifts, stands out as a relatively simple case, which could be exploited as a compact, robust, and low-cost atomic clock operating at a fractional frequency uncertainty of $10^{-17}$. With more experimental effort, the $^{223,225,226}$Ra$^+$ clocks could be pushed to a projected performance reaching the $10^{-18}$ level.

arXiv:1102.4988•Feb 24, 2011•0 citations

Potential of electric quadrupole transitions in radium isotopes for single-ion optical frequency standards

Oscar O. Versolato, L. W. Wansbeek, Klaus Peter Jungmann +3 more

We explore the potential of the electric quadrupole transitions $7s {}^{2}{S}_{1/2}$-$6d {}^{2}{D}_{3/2}$, $6d {}^{2}{D}_{5/2}$ in radium isotopes as single-ion optical frequency standards. The frequency shifts of the clock transitions due to external fields and the corresponding uncertainties are calculated. Several competitive ${}^{A}$Ra${}^{+}$ candidates, with $A=$ 223--229, are identified. In particular, we show that the transition $7s {}^{2}{S}_{1/2} (F=2,{m}_{F}=0)$-$6d {}^{2}{D}_{3/2} (F=0,{m}_{F}=0)$ at 828 nm in $^{223}\mathrm{Ra}$${}^{+}$, with no linear Zeeman and electric quadrupole shifts, stands out as a relatively simple case, which could be exploited as a compact, robust, and low-cost atomic clock operating at a fractional frequency uncertainty of ${10}^{\ensuremath{-}17}$. With more experimental effort, the $^{223,225,226}\mathrm{Ra}$${}^{+}$ clocks could be pushed to a projected performance reaching the ${10}^{\ensuremath{-}18}$ level.

Physical Review A•Apr 22, 2011•21 citations

Spectroscopy of electric dipole and quadrupole transitions in Ra + 224

Spencer Kofford, Haoran Li, Robert Kwapisz +5 more

We report on spectroscopy of the low-lying electronic transitions in $^{224}\mathrm{Ra}^{+}$. We measured the frequencies of the $^{2}S_{1/2}\ensuremath{\leftrightarrow}^{2}P_{1/2}$ cooling transition, the $^{2}S_{1/2}\ensuremath{\leftrightarrow}^{2}D_{5/2}$ clock transition, the $^{2}D_{3/2}\ensuremath{\leftrightarrow}^{2}P_{3/2}$ electric dipole transition, and the $^{2}D_{5/2}\ensuremath{\leftrightarrow}^{2}P_{3/2}$ cleanout transition. From these measurements we calculate the frequencies of the $^{2}D_{3/2}\ensuremath{\leftrightarrow}^{2}P_{1/2}$ repump transition, the $^{2}S_{1/2}\ensuremath{\leftrightarrow}^{2}D_{3/2}$ electric quadrupole transition, and the $^{2}S_{1/2}\ensuremath{\leftrightarrow}^{2}P_{3/2}$ electric dipole transition. The ion's low charge-to-mass ratio and convenient wavelengths make ${}^{224}{\mathrm{Ra}}^{+}$ a promising optical clock candidate.

arXiv:2409.09873•Physical Review A•Mar 4, 2025•2 citations

A multi-ion optical clock with $\mathbf{5 \times 10^{-19}}$ uncertainty

Melina Filzinger, Martin R. Steinel, Jian Jiang +4 more

Today's most accurate clocks are based on laser spectroscopy of electronic transitions in single trapped ions and feature fractional frequency uncertainties below $1\times10^{-18}$. Scaling these systems to multiple, simultaneously interrogated ions reduces measurement times, driving recent advances in multi-ion clocks. However, maintaining state-of-the-art systematic uncertainties while increasing the number of ions remains a central challenge. Here, we report on a multi-ion optical atomic clock with a fractional frequency uncertainty of $5.3\times10^{-19}$ and up to 10 \Sr ions. Ion-resolved state detection enables minimization of position-dependent shifts, with residual effects suppressed below the $10^{-20}$-level. Clock operation with eight to ten ions reduces the measurement time by a factor of 4.8 compared to single-ion operation. A comparison with an established \Yb single-ion clock yields an unperturbed frequency ratio of $0.6926711632159660405(20)$, with a statistical uncertainty of $0.9\times10^{-18}$ and a combined uncertainty of $2.9\times 10^{-18}$. These results demonstrate robust multi-ion clock operation with reduced averaging time and state-of-the-art accuracy.

physics.atom-phCross-listedarXiv:2603.23446•Mar 25, 2026•0 citations

The mercury-ion optical clock: towards a measurement of the quadrupole shift

Windell H. Oskay, A. Bartels, Scott A. Diddams +6 more

An optical clock based upon a single mercury ion in a radio-frequency trap has the potential for both high stability and high accuracy. The systematic uncertainty of this frequency standard is limited by contributions due to two types of external fields. The clock has previously been operated with a magnetic bias field that destabilizes dark states that limit the rates of laser cooling and state detection. This bias field has previously resulted in a substantial second-order Zeeman shift. We now destabilize the dark states with a polarization-scrambling technique that allows us to operate with only a minimal magnetic field. The second uncertainty that we address here is the magnitude of the quadrupole shift due to the interaction of stray electric-field gradients with the quadrupole moment of the ion. We describe the steps that we are taking to evaluate this shift in the near future. 1

European Frequency and Time Forum•Jan 1, 2004•2 citations

Ion optical clocks with three electronic states

C. A. Holliman, Mingyu Fan, Andrew M. Jayich

Optical clocks are the apotheosis of precision measurement, but they require frequent maintenance by scientists. The supporting laser systems are a particularly demanding component of these instruments. To reduce complexity and increase robustness we propose an optical clock with trapped alkali-like ions that use the S1/2 → D3/2 electric quadrupole transition. Compared to traditional group-II ion clocks this reduces the number of laser wavelengths required, and uses hyperfine state preparation and readout techniques enabled by the nuclear spin I = 1/2. We consider 225Ra+ as a candidate system for a clock with three electronic states, and discuss the potential to help realize a transportable optical clock.

arXiv:2211.05313•Optical and Quantum Sensing and Precision Metrology II•Mar 8, 2023•0 citations
We report the first operation of a Ra+{\mathrm{Ra}}^{+}Ra+ optical clock, a promising high-performance clock candidate. The clock uses a single trapped 226Ra+^{226}{\mathrm{Ra}}^{+}226Ra+ ion and operates on the 7s 2S1/2\ensuremath→6d 2D5/27s\text{ }^{2}{S}_{1/2}\ensuremath{\rightarrow}6d\text{ }^{2}{D}_{5/2}7s 2S1/2​\ensuremath→6d 2D5/2​ electric quadrupole transition. By self-referencing three pairs of symmetric Zeeman transitions, we demonstrate a frequency instability of 1.1\ifmmode×\else\texttimes\fi10\ensuremath−13/\ensuremathτ1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}/\sqrt{\ensuremath{\tau}}1.1\ifmmode×\else\texttimes\fi10\ensuremath−13/\ensuremathτ​, where \ensuremathτ\ensuremath{\tau}\ensuremathτ is the averaging time in seconds. The total systematic uncertainty is evaluated to be \ensuremathΔ\ensuremathν/\ensuremathν=9\ifmmode×\else\texttimes\fi10\ensuremath−16\mathrm{\ensuremath{\Delta}}\ensuremath{\nu}/\ensuremath{\nu}=9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\ensuremathΔ\ensuremathν/\ensuremathν=9\ifmmode×\else\texttimes\fi10\ensuremath−16. Using the clock, we realize the first measurement of the ratio of the D5/2{D}_{5/2}D5/2​ state to the S1/2{S}_{1/2}S1/2​ state Land'e ggg-factors: gD/gS=0.598 805 3(11){g}_{D}/{g}_{S}=0.598\text{ }805\text{ }3(11)gD​/gS​=0.598 805 3(11). A Ra+{\mathrm{Ra}}^{+}Ra+ optical clock could improve limits on the time variation of the fine structure constant, \ensuremathα\ifmmode˙\else\textperiodcentered\fi/\ensuremathα\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{\ensuremath{\alpha}}/\ensuremath{\alpha}\ensuremathα\ifmmode˙\else\textperiodcentered\fi​/\ensuremathα, in an optical frequency comparison. The ion also has several features that make it a suitable system for a transportable optical clock.
We explore the potential of the electric quadrupole transitions 7s 2S1/27s\,^2S_{1/2}7s2S1/2​ - 6d 2D3/26d\,^2D_{3/2}6d2D3/2​, 6d 2D5/26d\,^2D_{5/2}6d2D5/2​ in radium isotopes as single-ion optical frequency standards. The frequency shifts of the clock transitions due to external fields and the corresponding uncertainties are calculated. Several competitive A^AARa+^++ candidates with A=A=A= 223 - 229 are identified. In particular, we show that the transition 7s 2S1/2 (F=2,mF=0)7s\,^2S_{1/2}\,(F=2,m_F=0)7s2S1/2​(F=2,mF​=0) - 6d 2D3/2 (F=0,mF=0)6d\,^2D_{3/2}\,(F=0,m_F=0)6d2D3/2​(F=0,mF​=0) at 828 nm in 223^{223}223Ra+^++, with no linear Zeeman and electric quadrupole shifts, stands out as a relatively simple case, which could be exploited as a compact, robust, and low-cost atomic clock operating at a fractional frequency uncertainty of 10−1710^{-17}10−17. With more experimental effort, the 223,225,226^{223,225,226}223,225,226Ra+^++ clocks could be pushed to a projected performance reaching the 10−1810^{-18}10−18 level.
We explore the potential of the electric quadrupole transitions 7s2S1/27s {}^{2}{S}_{1/2}7s2S1/2​-6d2D3/26d {}^{2}{D}_{3/2}6d2D3/2​, 6d2D5/26d {}^{2}{D}_{5/2}6d2D5/2​ in radium isotopes as single-ion optical frequency standards. The frequency shifts of the clock transitions due to external fields and the corresponding uncertainties are calculated. Several competitive A{}^{A}ARa+{}^{+}+ candidates, with A=A=A= 223--229, are identified. In particular, we show that the transition 7s2S1/2(F=2,mF=0)7s {}^{2}{S}_{1/2} (F=2,{m}_{F}=0)7s2S1/2​(F=2,mF​=0)-6d2D3/2(F=0,mF=0)6d {}^{2}{D}_{3/2} (F=0,{m}_{F}=0)6d2D3/2​(F=0,mF​=0) at 828 nm in 223Ra^{223}\mathrm{Ra}223Ra+{}^{+}+, with no linear Zeeman and electric quadrupole shifts, stands out as a relatively simple case, which could be exploited as a compact, robust, and low-cost atomic clock operating at a fractional frequency uncertainty of ${10}^{\ensuremath{-}17}$. With more experimental effort, the 223,225,226Ra^{223,225,226}\mathrm{Ra}223,225,226Ra+{}^{+}+ clocks could be pushed to a projected performance reaching the ${10}^{\ensuremath{-}18}$ level.
We report on spectroscopy of the low-lying electronic transitions in 224Ra+^{224}\mathrm{Ra}^{+}224Ra+. We measured the frequencies of the $^{2}S_{1/2}\ensuremath{\leftrightarrow}^{2}P_{1/2}$ cooling transition, the $^{2}S_{1/2}\ensuremath{\leftrightarrow}^{2}D_{5/2}$ clock transition, the $^{2}D_{3/2}\ensuremath{\leftrightarrow}^{2}P_{3/2}$ electric dipole transition, and the $^{2}D_{5/2}\ensuremath{\leftrightarrow}^{2}P_{3/2}$ cleanout transition. From these measurements we calculate the frequencies of the $^{2}D_{3/2}\ensuremath{\leftrightarrow}^{2}P_{1/2}$ repump transition, the $^{2}S_{1/2}\ensuremath{\leftrightarrow}^{2}D_{3/2}$ electric quadrupole transition, and the $^{2}S_{1/2}\ensuremath{\leftrightarrow}^{2}P_{3/2}$ electric dipole transition. The ion's low charge-to-mass ratio and convenient wavelengths make 224Ra+{}^{224}{\mathrm{Ra}}^{+}224Ra+ a promising optical clock candidate.
A multi-ion optical clock with 5×10−19\mathbf{5 \times 10^{-19}}5×10−19 uncertainty
Today's most accurate clocks are based on laser spectroscopy of electronic transitions in single trapped ions and feature fractional frequency uncertainties below 1×10−181\times10^{-18}1×10−18. Scaling these systems to multiple, simultaneously interrogated ions reduces measurement times, driving recent advances in multi-ion clocks. However, maintaining state-of-the-art systematic uncertainties while increasing the number of ions remains a central challenge. Here, we report on a multi-ion optical atomic clock with a fractional frequency uncertainty of 5.3×10−195.3\times10^{-19}5.3×10−19 and up to 10 \Sr ions. Ion-resolved state detection enables minimization of position-dependent shifts, with residual effects suppressed below the 10−2010^{-20}10−20-level. Clock operation with eight to ten ions reduces the measurement time by a factor of 4.8 compared to single-ion operation. A comparison with an established \Yb single-ion clock yields an unperturbed frequency ratio of 0.6926711632159660405(20)0.6926711632159660405(20)0.6926711632159660405(20), with a statistical uncertainty of 0.9×10−180.9\times10^{-18}0.9×10−18 and a combined uncertainty of 2.9×10−182.9\times 10^{-18}2.9×10−18. These results demonstrate robust multi-ion clock operation with reduced averaging time and state-of-the-art accuracy.
An optical clock based upon a single mercury ion in a radio-frequency trap has the potential for both high stability and high accuracy. The systematic uncertainty of this frequency standard is limited by contributions due to two types of external fields. The clock has previously been operated with a magnetic bias field that destabilizes dark states that limit the rates of laser cooling and state detection. This bias field has previously resulted in a substantial second-order Zeeman shift. We now destabilize the dark states with a polarization-scrambling technique that allows us to operate with only a minimal magnetic field. The second uncertainty that we address here is the magnitude of the quadrupole shift due to the interaction of stray electric-field gradients with the quadrupole moment of the ion. We describe the steps that we are taking to evaluate this shift in the near future. 1
Optical clocks are the apotheosis of precision measurement, but they require frequent maintenance by scientists. The supporting laser systems are a particularly demanding component of these instruments. To reduce complexity and increase robustness we propose an optical clock with trapped alkali-like ions that use the S1/2 → D3/2 electric quadrupole transition. Compared to traditional group-II ion clocks this reduces the number of laser wavelengths required, and uses hyperfine state preparation and readout techniques enabled by the nuclear spin I = 1/2. We consider 225Ra+ as a candidate system for a clock with three electronic states, and discuss the potential to help realize a transportable optical clock.