Speaker
Description
The 229mTh isomeric state has the lowest known energy for a nuclear transition and is a candidate for a clock disciplined by an atomic nucleus. After demonstrating the absolute transition frequency measurement, we now move on to characterizing its environmental sensitivity as a clock, and present preliminary results regarding the effect of resonant microwaves. A clock based on this transition would be sensitive to nuclear and beyond standard model physics[1], while performing as a solid-state clock[2].
Keywords—clock; nuclear; spectroscopy; fundamental physics; crystal
Due to the insensitive nature of the nucleus to the chemical environment, the host atom may be doped into a crystal[3] in order to obtain many orders of magnitude more oscillators probed than other platforms, while still maintaining a narrow linewidth; untrue for electrical transitions. This being said, narrow atomic transitions such as those in ion or quantum gas platforms have made strides both as frequency references and stringent tests of the standard model. [4]
Nuclear energy levels are set by competition between the coulomb force and the strong force. If fundamental constants were changing over time, one could expect that the fortuitous cancellation of Coulomb and strong nuclear forces resulting in the low energy isomeric state would change, resulting in a different nuclear clock operation frequency, detectable by a clock based on coulomb force.
We characterize the effect the calcium fluoride host crystal environment has on the nuclear transition.[5] This allows us to extract both crystal and nuclear parameters, vital for understanding the performance of a nuclear clock. We also present a measurement of the long-term stability of the transition.[6]
The laser used is a VUV frequency comb generated via the 7th harmonic of an IR comb. The comb is locked to the JILA strontium clock, allowing a stable reference for measuring small changes in frequency due to doping concentration or temperature.[7]
A “zero shift temperature” is identified, where there is zero first order shift in frequency due to fluctuations in temperature. We will also present preliminary results on the effect of microwave frequencies resonant with the splitting due to the interaction between the nuclear quadrupole moment and the electric field gradient within the crystal.
REFERENCES
[1] K. Beeks et al., “Fine-structure constant sensitivity of the Th-229 nuclear clock transition,” Jul. 24, 2024, arXiv: arXiv:2407.17300. doi: 10.48550/arXiv.2407.17300.
[2] E. Peik and C. Tamm, “Nuclear laser spectroscopy of the 3.5 eVtransition in Th-229,” EPL, vol. 61, no. 2, p. 181, Jan. 2003, doi: 10.1209/epl/i2003-00210-x.
[3] K. Beeks et al., “Optical transmission enhancement of ionic crystals via superionic fluoride transfer: Growing VUV-transparent radioactive crystals,” Phys. Rev. B, vol. 109, no. 9, p. 094111, Mar. 2024, doi: 10.1103/PhysRevB.109.094111.
[4] A. D. Ludlow, M. M. Boyd, J. Ye, E. Peik, and P. O. Schmidt, “Optical atomic clocks,” Rev. Mod. Phys., vol. 87, no. 2, pp. 637–701, Jun. 2015, doi: 10.1103/RevModPhys.87.637.
[5] J. S. Higgins et al., “Temperature sensitivity of a Thorium-229 solid-state nuclear clock,” Sep. 17, 2024, arXiv: arXiv:2409.11590. doi: 10.48550/arXiv.2409.11590.
[6] T. Ooi et al., “Frequency reproducibility of solid-state Th-229 nuclear clocks,” Jul. 01, 2025, arXiv: arXiv:2507.01180. doi: 10.48550/arXiv.2507.01180.
[7] C. Zhang et al., “Frequency ratio of the 229mTh nuclear isomeric transition and the 87Sr atomic clock,” Nature, vol. 633, no. 8028, pp. 63–70, Sep. 2024, doi: 10.1038/s41586-024-07839-6.
