Abstract
An inner-shell orbital clock transition 1S0 ↔ 4f135d6s2 (J = 2) in neutral ytterbium atoms has attracted much attention as a new optical frequency standard as well as a highly sensitive probe for several new physics phenomena, such as ultralight dark matter, violation of local Lorentz invariance, and a new Yukawa potential between electrons and neutrons. Here we demonstrate almost two-orders-of-magnitude improvement in precision spectroscopy over previous reports on this transition, achieved by trapping atoms in a three-dimensional magic-wavelength optical lattice. In particular, we successfully observe the coherent Rabi oscillation, the relaxation dynamics of the excited state and the interorbital Feshbach resonance. To highlight the high precision of our spectroscopy, we carry out precise isotope shift measurements between five stable bosonic isotopes well below 10-Hz uncertainties, successfully setting bounds for a hypothetical boson mediating a force between electrons and neutrons. These results open up the way for various new physics search experiments and a wide range of applications to quantum science with this clock transition.
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Acknowledgements
We thank A. Vutha, T. Naito and N. Ozawa for useful discussions. This work was supported by the Grant-in-Aid for Scientific Research of JSPS (JP17H06138, JP18H05405, JP18H05228, JP21H01014, JP22K20356, 24K16995, 24KJ1347 and 24K07018), JST PRESTO (JP-MJPR23F5), JST CREST (JPMJCR1673 and JP-MJCR23I3), MEXT Quantum Leap Flagship Program (MEXT Q-LEAP) grant JPMXS0118069021, JST Moon-shot R&D (JPMJMS2268 and JP-MJMS2269) and JST ASPIRE (JPMJAP24C2). K.O. acknowledges support from the Graduate School of Science, Kyoto University, under the Ginpu Fund. A.S. acknowledges financial support from the JSPS KAKENHI (21K14643). The work of Y.Y. was supported by the National Science and Technology Council, the Ministry of Education (Higher Education Sprout Project NTU-112L104022), and the National Center for Theoretical Sciences of Taiwan. We used the supercomputer of ACCMS, Kyoto University (Service Course and Collaborative Research Project for Enhancing Performance of Programming), and the computer resource offered under the category of General Projects by the Research Institute for Information Technology, Kyushu University.
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T.I., K.O., H.K., T.T. and R.A. carried out the experiments. T.I., K.O., Y.Y. and M.T. implemented the data analysis. A.S. carried out the atomic theoretical calculation. Y.T. supervised the whole project. All the authors contributed to the writing of the manuscript.
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Extended data
Extended Data Fig. 1 Schematic diagram of the BBR quenching of the \(\left|e\right\rangle\) state.
In this figure, we show the case where the \(\left|e\right\rangle\) state is excited to \(\left|i\right\rangle {=}^{1}{D}_{2}\,({m}_{J}=+1)\) by BBR.
Extended Data Fig. 2 Time traces of IS measurements.
a–d, Each panel presents the result for a specific isotope pair: 168Yb–174Yb (a), 170Yb–174Yb (b), 172Yb–174Yb (c) and 176Yb–174Yb (d). A blue data point is the mean value of each segment after the systematic correction, while an error bar shows the overlapping Allan deviation. Blue (orange) shaded regions represent the 1σ statistical (systematic) uncertainties. Note that d is the same as Fig. 3b.
Extended Data Fig. 3 Lattice light shift.
The measured ISs \(\delta {\nu }_{431}^{A,174}\) are plotted with respect to the lattice depth per axis, where A = 168 (a), 170 (b), 172 (c), and 176 (d). Points and error bars denote the mean values and the 1σ statistical uncertainties, respectively, with the latter derived from the overlapping Allan deviations. Green solid lines are fitting curves by equation (17) and the determined y-axis intercepts are subtracted from the data. During the measurement, we keep the lattice depth ratio for the three axes. To satisfy the Lamb-Dicke condition, the lattice depth per axis is set to be more than 15Er, at which the Lamb-Dicke factor is 0.66.
Extended Data Fig. 4 Investigation of the quadratic Zeeman shift.
The magnetic field dependences of \(\delta {\nu }_{431}^{A,174}\) are shown, where A = 168 (a), 170 (b), 172 (c), and 176 (d). Points and error bars denote the mean values and the 1σ statistical uncertainties, respectively, with the latter derived from the overlapping Allan deviations. Green shaded regions represent the average of error bars, while orange shaded areas denote the standard deviation of three or four data points.
Extended Data Fig. 5 Investigation of the probe light shift.
The probe laser intensity dependences of \(\delta {\nu }_{431}^{A,174}\) are shown, where A = 168 (a), 170 (b), 172 (c), and 176 (d). Points and error bars denote the mean values and the 1σ statistical uncertainties, respectively, with the latter derived from the overlapping Allan deviations. The definitions of the two shaded areas are the same as Extended Data Fig. 4.
Extended Data Fig. 6 PS electronic factor Xi for six transitions.
The calculated values of Xi are plotted as a function of the new-particle mass mϕ.
Supplementary information
Supplementary Information (download PDF )
Supplementary sections I–V, Supplementary Figs. 1–4, Supplementary Tables 1–11 and Supplementary Discussion.
Source data
Source Data Fig. 1 (download XLSX )
A typical spectrum.
Source Data Fig. 2 (download XLSX )
Basic properties of the new clock transition.
Source Data Fig. 3 (download XLSX )
IS measurements.
Source Data Fig. 4 (download XLSX )
King plot analysis.
Source Data Fig. 5 (download XLSX )
Constraints on nuclear factors by the dual King plot analysis.
Source Data Extended Data Fig. 2 (download XLSX )
Time traces of IS measurements.
Source Data Extended Data Fig. 3 (download XLSX )
Lattice light shift.
Source Data Extended Data Fig. 4 (download XLSX )
Investigation of the quadratic Zeeman shift.
Source Data Extended Data Fig. 5 (download XLSX )
Investigation of the probe light shift.
Source Data Extended Data Fig. 6 (download XLSX )
PS electronic factor Xi for six transitions.
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Ishiyama, T., Ono, K., Kawase, H. et al. Orders-of-magnitude improvement in precision spectroscopy of an inner-shell orbital clock transition in neutral ytterbium. Nat. Photon. (2026). https://doi.org/10.1038/s41566-026-01857-8
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DOI: https://doi.org/10.1038/s41566-026-01857-8
