Speaker
Description
Highly charged ions (HCI) are promising candidates for novel optical clocks with applications in frequency metrology and tests of fundamental physics [1]. Typically, megakelvin-range temperatures needed to produce HCI hinder high-precision spectroscopy. To overcome this, we extract HCI from an electron beam ion trap (EBIT) and transfer them to a cryogenic linear Paul trap. There, single HCI are sympathetically cooled by laser-cooled Be$^{+}$ ions down to millikelvin temperatures, thus enabling quantum logic state readout [2]. We demonstrated in this way an optical clock based on Ar$^{13+}$, and determined its absolute frequency with sub-Hz uncertainty [3] against the Yb$^+$ octupole ion clock at PTB [4]. Our techniques are readily applicable to many ions, e. g. Ca$^{14+}$ [5] as well as Xe HCI [6]. Recently, we determined the isotope shift of a narrow M1 transition in stable even isotopes of Ca$^{14+}$ with 150 mHz accuracy. We combine these results with available isotope-shift data of Ca$^+$ [7] in a King plot which is sensitive to a new force that would couple electrons and neutrons [8,9]. In this way, we strengthen the constraints on the existence of such a hypothetical interaction by a factor of about five as compared to previous studies [7]. We also estimate how far improved measurements of Ca isotope masses and isotope shifts of the Ca$^+$ S$_{1/2}$ - D$_{5/2}$ transition would enhance such constraints.
[1] M. Kozlov, et al., Rev. Mod. Phys., 90, 045005 (2018)
[2] P. Micke, T. Leopold, S.A. King et al., Nature 578 (2020)
[3] S. A. King, L. J. Spiess, et al., Nature 611, 43 (2022)
[4] R. Lange et al., Phys. Rev. Lett. 126, 011102 (2021)
[5] N. Rehbehn, et al., Phys. Rev. A 103, L040801 (2021)
[6] N. Rehbehn, et al., Phys. Rev. Lett. 131, 161803 (2023)
[7] T. T. Chang et al., arXiv:2311.17337v1, 123003 (2023)
[8] J. C. Berengut, et al., Phys. Rev. Lett. 120, 091801 (2018)
[9] J. C. Berengut, et al., Phys. Rev. Research 2 043444 (2020)
