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Frequency ratio of the 229mTh nuclear isomeric transition and the 87Sr atomic clock

Nature volume 633, pages 63–70 (2024)Cite this article

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Abstract

Optical atomic clocks1,2 use electronic energy levels to precisely keep track of time. A clock based on nuclear energy levels promises a next-generation platform for precision metrology and fundamental physics studies. Thorium-229 nuclei exhibit a uniquely low-energy nuclear transition within reach of state-of-the-art vacuum ultraviolet (VUV) laser light sources and have, therefore, been proposed for construction of a nuclear clock3,4. However, quantum-state-resolved spectroscopy of the 229mTh isomer to determine the underlying nuclear structure and establish a direct frequency connection with existing atomic clocks has yet to be performed. Here, we use a VUV frequency comb to directly excite the narrow 229Th nuclear clock transition in a solid-state CaF2 host material and determine the absolute transition frequency. We stabilize the fundamental frequency comb to the JILA 87Sr clock2 and coherently upconvert the fundamental to its seventh harmonic in the VUV range by using a femtosecond enhancement cavity. This VUV comb establishes a frequency link between nuclear and electronic energy levels and allows us to directly measure the frequency ratio of the 229Th nuclear clock transition and the 87Sr atomic clock. We also precisely measure the nuclear quadrupole splittings and extract intrinsic properties of the isomer. These results mark the start of nuclear-based solid-state optical clocks and demonstrate the first comparison, to our knowledge, of nuclear and atomic clocks for fundamental physics studies. This work represents a confluence of precision metrology, ultrafast strong-field physics, nuclear physics and fundamental physics.

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Fig. 1: VUV comb spectroscopy of the 229Th nuclear clock transition.
Fig. 2: A full-range comb scan.
Fig. 3: Line shape and centre frequency determination.
Fig. 4: Absolute frequency determination.
Fig. 5: Direct spectroscopic measurement of nuclear electric quadrupole structure.

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Data availability

The data that support the findings of this study are available from the corresponding author upon appropriate request.

References

  1. Ludlow, A. D., Boyd, M. M., Ye, J., Peik, E. & Schmidt, P. O. Optical atomic clocks. Rev. Mod. Phys. 87, 637–701 (2015).

    Article  ADS  CAS  Google Scholar 

  2. Aeppli, A., Kim, K., Warfield, W., Safronova, M. S. & Ye, J. Clock with 8 × 10−19 systematic uncertainty. Phys. Rev. Lett. 133, 023401 (2024).

  3. Peik, E. & Tamm, C. Nuclear laser spectroscopy of the 3.5 eV transition in Th-229. EPL – Europhys. Lett. 61, 181 (2003).

    Article  ADS  CAS  Google Scholar 

  4. Tkalya, E. V., Varlamov, V. O., Lomonosov, V. V. & Nikulin, S. A. Processes of the nuclear isomer 229mTh(3/2+, 3.5 ± 1.0 eV) resonant excitation by optical photons. Phys. Scr. 53, 296 (1996).

    Article  ADS  CAS  Google Scholar 

  5. Bothwell, T. et al. Resolving the gravitational redshift across a millimetre-scale atomic sample. Nature 602, 420–424 (2022).

    Article  ADS  CAS  PubMed  Google Scholar 

  6. Ye, J. & Zoller, P. Essay: quantum sensing with atomic, molecular, and optical platforms for fundamental physics. Phys. Rev. Lett. 132, 190001 (2024).

    Article  ADS  CAS  PubMed  Google Scholar 

  7. von der Wense, L. & Seiferle, B. The 229Th isomer: prospects for a nuclear optical clock. Eur. Phys. J. A 56, 277 (2020).

    Article  ADS  Google Scholar 

  8. Peik, E. et al. Nuclear clocks for testing fundamental physics. Quantum Sci. Technol. 6, 034002 (2021).

    Article  ADS  Google Scholar 

  9. Beeks, K. et al. The thorium-229 low-energy isomer and the nuclear clock. Nat. Rev. Phys. 3, 238–248 (2021).

    Article  CAS  Google Scholar 

  10. Flambaum, V. V. Enhanced effect of temporal variation of the fine structure constant and the strong interaction in 229Th. Phys. Rev. Lett. 97, 092502 (2006).

    Article  ADS  CAS  PubMed  Google Scholar 

  11. Fadeev, P., Berengut, J. C. & Flambaum, V. V. Sensitivity of 229Th nuclear clock transition to variation of the fine-structure constant. Phys. Rev. A 102, 052833 (2020).

    Article  ADS  CAS  Google Scholar 

  12. Nickerson, B. S. et al. Driven electronic bridge processes via defect states in 229Th-doped crystals. Phys. Rev. A 103, 053120 (2021).

    Article  ADS  CAS  Google Scholar 

  13. Helmer, R. G. & Reich, C. W. An excited state of 229Th at 3.5 eV. Phys. Rev. C 49, 1845–1858 (1994).

    Article  ADS  CAS  Google Scholar 

  14. Guimarães-Filho, Z. O. & Helene, O. Energy of the 3/2+ state of 229Th reexamined. Phys. Rev. C 71, 044303 (2005).

    Article  ADS  Google Scholar 

  15. Beck, B. R. et al. Energy splitting of the ground-state doublet in the nucleus 229Th. Phys. Rev. Lett. 98, 142501 (2007).

    Article  ADS  CAS  PubMed  Google Scholar 

  16. Beck, B. R. et al. Improved Value for the Energy Splitting of the Ground-State Doublet in the Nucleus 229mTh Report No. LLNL-PROC-415170 (Lawrence Livermore National Laboratory, 2009).

  17. Thielking, J. et al. Laser spectroscopic characterization of the nuclear-clock isomer 229mTh. Nature 556, 321–325 (2018).

    Article  ADS  CAS  PubMed  Google Scholar 

  18. Seiferle, B. et al. Energy of the 229Th nuclear clock transition. Nature 573, 243–246 (2019).

    Article  ADS  CAS  PubMed  Google Scholar 

  19. Masuda, T. et al. X-ray pumping of the 229Th nuclear clock isomer. Nature 573, 238–242 (2019).

    Article  ADS  CAS  PubMed  Google Scholar 

  20. Yamaguchi, A. et al. Energy of the 229Th nuclear clock isomer determined by absolute γ-ray energy difference. Phys. Rev. Lett. 123, 222501 (2019).

    Article  ADS  CAS  PubMed  Google Scholar 

  21. Sikorsky, T. et al. Measurement of the 229Th isomer energy with a magnetic microcalorimeter. Phys. Rev. Lett. 125, 142503 (2020).

    Article  ADS  CAS  PubMed  Google Scholar 

  22. von der Wense, L. et al. Direct detection of the 229Th nuclear clock transition. Nature 533, 47–51 (2016).

    Article  ADS  PubMed  Google Scholar 

  23. Kraemer, S. et al. Observation of the radiative decay of the 229Th nuclear clock isomer. Nature 617, 706–710 (2023).

    Article  ADS  CAS  PubMed  Google Scholar 

  24. Hiraki, T. et al. Controlling 229Th isomeric state population in a VUV transparent crystal. Nat. Commun. 15, 5536 (2024).

  25. Yamaguchi, A. et al. Laser spectroscopy of triply charged 229Th isomer for a nuclear clock. Nature 629, 62–66 (2024).

    Article  ADS  CAS  PubMed  Google Scholar 

  26. Tiedau, J. et al. Laser excitation of the Th-229 nucleus. Phys. Rev. Lett. 132, 182501 (2024).

    Article  ADS  CAS  PubMed  Google Scholar 

  27. Elwell, R. et al. Laser excitation of the 229Th nuclear isomeric transition in a solid-state host. Phys. Rev. Lett. 133, 013201 (2024).

    Article  CAS  PubMed  Google Scholar 

  28. Tkalya, E. V. Spontaneous emission probability for M1 transition in a dielectric medium: 229mTh (3/2+, 3.5±1.0 eV) decay. JETP Lett. 71, 311–313 (2000).

    Article  ADS  CAS  Google Scholar 

  29. Rellergert, W. G. et al. Constraining the evolution of the fundamental constants with a solid-state optical frequency reference based on the 229Th nucleus. Phys. Rev. Lett. 104, 200802 (2010).

    Article  ADS  PubMed  Google Scholar 

  30. Kazakov, G. A. et al. Performance of a 229Thorium solid-state nuclear clock. New J. Phys. 14, 083019 (2012).

    Article  ADS  Google Scholar 

  31. Oelker, E. et al. Demonstration of 4.8 × 10−17 stability at 1 s for two independent optical clocks. Nat. Photon. 13, 714–719 (2019).

    Article  ADS  CAS  Google Scholar 

  32. Milner, W. R. et al. Demonstration of a timescale based on a stable optical carrier. Phys. Rev. Lett. 123, 173201 (2019).

    Article  ADS  CAS  PubMed  Google Scholar 

  33. Diddams, S. A., Vahala, K. & Udem, T. Optical frequency combs: coherently uniting the electromagnetic spectrum. Science 369, eaay3676 (2020).

    Article  CAS  PubMed  Google Scholar 

  34. Dreissen, L. S. et al. High-precision Ramsey-comb spectroscopy based on high-harmonic generation. Phys. Rev. Lett. 123, 143001 (2019).

    Article  ADS  CAS  PubMed  Google Scholar 

  35. Jones, R. J., Moll, K. D., Thorpe, M. J. & Ye, J. Phase-coherent frequency combs in the vacuum ultraviolet via high-harmonic generation inside a femtosecond enhancement avity. Phys. Rev. Lett. 94, 193201 (2005).

    Article  ADS  PubMed  Google Scholar 

  36. Gohle, C. et al. A frequency comb in the extreme ultraviolet. Nature 436, 234–237 (2005).

    Article  ADS  CAS  PubMed  Google Scholar 

  37. Cingöz, A. et al. Direct frequency comb spectroscopy in the extreme ultraviolet. Nature 482, 68–71 (2012).

    Article  ADS  PubMed  Google Scholar 

  38. Benko, C. et al. Extreme ultraviolet radiation with coherence time greater than 1 s. Nat. Photon. 8, 530–536 (2014).

    Article  ADS  CAS  Google Scholar 

  39. Pupeza, I., Zhang, C., Högner, M. & Ye, J. Extreme-ultraviolet frequency combs for precision metrology and attosecond science. Nat. Photon. 15, 175–186 (2021).

    Article  ADS  CAS  Google Scholar 

  40. Zhang, C. et al. Tunable VUV frequency comb for 229mTh nuclear spectroscopy. Opt. Lett. 47, 5591 (2022).

    Article  ADS  CAS  PubMed  Google Scholar 

  41. Ycomb - Compact frequency comb. IMRA https://www.imra.com/products/imra-scientific/ycomb-100 (2021).

  42. Pronin, O. et al. Ultrabroadband efficient intracavity XUV output coupler. Opt. Express 19, 10232–10240 (2011).

    Article  ADS  PubMed  Google Scholar 

  43. Fischer, J. et al. Efficient XUV-light out-coupling of intra-cavity high harmonics by a coated grazing-incidence plate. Opt. Express 30, 30969–30979 (2022).

    Article  ADS  CAS  PubMed  Google Scholar 

  44. Beeks, K. et al. Growth and characterization of thorium-doped calcium fluoride single crystals. Sci. Rep. 13, 3897 (2023).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  45. Beeks, K. et al. Optical transmission enhancement of ionic crystals via superionic fluoride transfer: growing VUV-transparent radioactive crystals. Phys. Rev. B 109, 094111 (2024).

    Article  ADS  CAS  Google Scholar 

  46. Stellmer, S., Schreitl, M. & Schumm, T. Radioluminescence and photoluminescence of Th:CaF2 crystals. Sci. Rep. 5, 15580 (2015).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  47. Dessovic, P. et al. 229Thorium-doped calcium fluoride for nuclear laser spectroscopy. J. Phys. Condens. Matter 26, 105402 (2014).

    Article  CAS  PubMed  Google Scholar 

  48. Dunlap, B. D. & Kalvius, G. M. in Handbook on the Physics and Chemistry of the Actinides Vol. 2 (eds Freeman, A. J. & Lander, G. H.) 331–434 (Elsevier Science, 1985).

  49. Porsev, S. G., Safronova, M. S. & Kozlov, M. G. Precision calculation of hyperfine constants for extracting nuclear moments of 229Th. Phys. Rev. Lett. 127, 253001 (2021).

    Article  ADS  CAS  PubMed  Google Scholar 

  50. von der Wense, L. & Zhang, C. Concepts for direct frequency-comb spectroscopy of 229mTh and an internal-conversion-based solid-state nuclear clock. Eur. Phys. J. D 74, 146 (2020).

    Article  ADS  Google Scholar 

  51. Travers, J. C., Grigorova, T. F., Brahms, C. & Belli, F. High-energy pulse self-compression and ultraviolet generation through soliton dynamics in hollow capillary fibres. Nat. Photon. 13, 547–554 (2019).

    Article  ADS  CAS  Google Scholar 

  52. Liao, W.-T., Das, S., Keitel, C. H. & Pálffy, A. Coherence-enhanced optical determination of the 229Th isomeric transition. Phys. Rev. Lett. 109, 262502 (2012).

    Article  ADS  PubMed  Google Scholar 

  53. Jain, A. et al. Commentary: The Materials Project: A materials genome approach to accelerating materials innovation. APL Mater. 1, 011002 (2013).

  54. Sinclair, L. C. et al. Invited article: a compact optically coherent fiber frequency comb. Rev. Sci. Instrum. 86, 081301 (2015).

    Article  ADS  CAS  PubMed  Google Scholar 

  55. Black, E. D. An introduction to Pound–Drever–Hall laser frequency stabilization. Am. J. Phys. 69, 79–87 (2001).

    Article  ADS  Google Scholar 

  56. Allison, T. K., Cingöz, A., Yost, D. C. & Ye, J. Extreme nonlinear optics in a femtosecond enhancement cavity. Phys. Rev. Lett. 107, 183903 (2011).

    Article  ADS  CAS  PubMed  Google Scholar 

  57. Yost, D. C. et al. Power optimization of XUV frequency combs for spectroscopy applications [Invited]. Opt. Express 19, 23483–23493 (2011).

    Article  ADS  CAS  PubMed  Google Scholar 

  58. Beeks, K. The nuclear excitation of thorium-229 in the CaF2 environment: development of a crystalline nuclear clock. PhD thesis, Technische Universität, Wien (2022).

  59. Rix, S. et al. Formation of metallic colloids in CaF2 by intense ultraviolet light. Appl. Phys. Lett. 99, 261909–261909 (2011).

    Article  ADS  Google Scholar 

  60. Seiferle, B., von der Wense, L., Laatiaoui, M. & Thirolf, P. G. A VUV detection system for the direct photonic identification of the first excited isomeric state of 229Th. Eur. Phys. J. D 70, 58 (2016).

    Article  ADS  Google Scholar 

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Acknowledgements

We thank K. Kim, A. Aeppli, W. Warfield and W. Milner for building and maintaining the JILA 87Sr optical clock; D. Lee, Z. Hu and B. Lewis for building and maintaining the JILA stable laser and the cryogenic Si cavity; the entire crystal growth team at TU Wien for preparation of the thorium-doped crystal; M. E. Fermann and J. Jiang for help in constructing the high-power infrared frequency comb; K. Hagen, C. Schwadron, K. Thatcher, H. Green, D. Warren and J. Uhrich for help in designing and building mechanical parts used in the detection setup; T. Brown and I. Rýger for help in designing and making electronics used in the experiment; M. Ashton, B. C. Denton and M. R. Statham for help in the shipment of radioactive samples; E. Hudson, E. Peik, J. Hur, J. Thompson, J. Weitenberg and A. Ozawa for helpful discussions; and IMRA America for collaboration. We acknowledge funding support from the Army Research Office (grant no. W911NF2010182), the Air Force Office of Scientific Research (grant no. FA9550-19-1-0148), the National Science Foundation (grant no. QLCI OMA-2016244), the National Science Foundation (grant no. PHY-2317149) and the National Institute of Standards and Technology. J.S.H. acknowledges support from a National Research Council Postdoctoral Fellowship. L.v.d.W. acknowledges funding from a Feodor Lynen fellowship from the Humboldt Foundation. P.G.T. acknowledges support from the European Research Council (Horizon 2020, grant no. 856415) and the European Union’s Horizon 2020 Programme (grant no. 664732). The 229Th:CaF2 crystal was grown in TU Wien with support from the European Research Council (Horizon 2020, grant no. 856415) and the Austrian Science Fund (grant DOI: 10.55776/F1004, 10.55776/J4834 and 10.55776/ PIN9526523). The project 23FUN03 HIOC (grant DOI: 10.13039/100019599) has received funding from the European Partnership on Metrology, co-financed from the European Union’s Horizon Europe Research and Innovation Programme and by the participating states. We thank the National Isotope Development Center of DoE and Oak Ridge National Laboratory for providing the Th-229 used in this work.

Author information

Author notes

  1. Lars von der Wense

    Present address: Johannes Gutenberg-Universität Mainz, Institut für Physik, Mainz, Germany

  2. Kjeld Beeks

    Present address: Laboratory for Ultrafast Microscopy and Electron Scattering (LUMES), Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland

Authors and Affiliations

  1. JILA, University of Colorado Boulder, Boulder, CO, USA

    Chuankun Zhang, Tian Ooi, Jacob S. Higgins, Jack F. Doyle, Lars von der Wense & Jun Ye

  2. NIST, Boulder, CO, USA

    Chuankun Zhang, Tian Ooi, Jacob S. Higgins, Jack F. Doyle, Lars von der Wense & Jun Ye

  3. Department of Physics, University of Colorado Boulder, Boulder, CO, USA

    Chuankun Zhang, Tian Ooi, Jacob S. Higgins, Jack F. Doyle, Lars von der Wense & Jun Ye

  4. Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Vienna, Austria

    Kjeld Beeks, Adrian Leitner, Georgy A. Kazakov & Thorsten Schumm

  5. IMRA America, Ann Arbor, MI, USA

    Peng Li

  6. Ludwig-Maximilians-Universität München, Garching, Germany

    Peter G. Thirolf

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Contributions

C.Z., T.O., J.S.H., J.F.D., L.v.d.W., K.B., T.S. and J.Y. conceived and planned the experiment; K.B., A.L., G.A.K. and T.S. grew the thorium-doped crystal and characterized its performance; P.G.T. provided valuable insight and the parabolic mirror; and C.Z., T.O., J.S.H., J.F.D., L.v.d.W., P.L. and J.Y. performed the measurement and analysed the data. All authors wrote the manuscript.

Corresponding authors

Correspondence to Chuankun Zhang or Jun Ye.

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Extended data figures and tables

Extended Data Fig. 1 Locking scheme used in our experimental setup.

A Yb-fiber oscillator is used to generate the fundamental frequency comb40. The light is amplified using a chirped pulse amplification scheme in a large mode area gain fiber. The output comb light (average power 40–50 W) is coupled to a femtosecond enhancement cavity with finesse ~600 to further enhance the peak power for efficient cavity-enhanced high harmonic generation. The 7th harmonic is outcoupled using a grazing incidence plate42,43 (GIP) and directed to the sample chamber. A portion of the pre-amplified comb light is picked off and focused to a highly nonlinear photonic crystal fiber (HNL PCF) for broadband supercontinuum generation. The light is also doubled using a periodically poled lithium niobate (PPLN) crystal. These two beams generate a beatnote that directly reports on fCEO (f–2 f detection), which can be fed back to the pump current for fCEO locking. The supercontinuum light is beatnote locked against the Sr clock light at 698 nm through an auxiliary narrow linewidth Mephisto laser at 1064 nm. The beatnote fbeat is mixed with a DDS output and is used to steer the Mephisto laser frequency. The Mephisto output is passed through a fiber acousto-optic modulator (AOM) to generate a frequency offset and is beat against a portion of the preamplified fundamental comb light. The control signal is fed back to the oscillator cavity length to close the loop for the fbeat lock. We conduct our scans by changing the DDS offset frequency, which ultimately changes the comb repetition frequency without shifting fCEO. An additional portion of the Mephisto light is picked off and modulated with an electro-optical modulator (EOM) for Pound-Drever-Hall locking of the enhancement cavity. The offset between the locked cavity resonance and the fundamental frequency comb can be tuned by adjusting the AOM offset frequency to mitigate intracavity plasma instabilities56,57. PZT, piezo-electric actuator.

Extended Data Table 1 Properties of Tiny-X2 crystal
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Zhang, C., Ooi, T., Higgins, J.S. et al. Frequency ratio of the 229mTh nuclear isomeric transition and the 87Sr atomic clock. Nature 633, 63–70 (2024). https://doi.org/10.1038/s41586-024-07839-6

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