Speaker
Description
Singly ionized lutetium (176Lu+) is a unique clock candidate with several attractive features for clock applications [1-6]. It provides three independent clock transitions allowing consistency checks of error budgets through frequency comparisons within the one system [6]. Recently, the systematic uncertainties of two lutetium frequency references have been calibrated to the mid 10-19 fractionally on the 848-nm transition. Subsequent comparison via correlation spectroscopy, demon-strated inaccuracy to low 10-18 level limited by statistical uncertainty [1]. The absolute frequency measurement of 848-nm clock transition has been measured with a fractional uncertainty of 1.8×10−15 limited by our available realization of the second.
To realize the full potential lutetium has to offer requires an assessment of the 804-nm clock transi-tion to a comparable level as the 848-nm transition. The two most challenging aspects of this are the blackbody radiation (BBR) shift and the residual quadrupole moment. The larger BBR shift of the 804-nm transition requires inaccuracy of the scalar differential polarizability at the 1% level. We plan to achieve this through comparison measurement with Ba+ as proposed in [7], for which the required measurements have been made [8]. The residual quadrupole moment arises from cou-pling between fine-structure levels resulting in imperfect cancellation via hyperfine averaging [9]. The effect is expected to give a shift at the low 10-19 as for the 848-nm transition and we plan to in-vestigate this through high accuracy measurements of differential quadrupole moments and g-fac-tors [9,10].
Absolute frequency accuracy requires an assessment of the system temperature, and this requires temperature calibration at the level of a few degrees for the 804-nm transition. However, for appli-cations requiring only a comparison, such as height referencing, it is only a temperature difference that matters. For lutetium this can be assessed through measurement of the frequency ratio between the 804-nm and 848-nm transitions within each apparatus.
References
[1] Zhiqiang Zhang, et al., “176Lu+ clock comparison at the 10−18 level via correlation spectroscopy”, Sci. Adv. 9, eadg1971, 2023.
[2] M. D. Barrett, “Developing a field independent frequency reference”, New J. Phys, 17(5):053024, 2015.
[3] K. J. Arnold, et al, “Blackbody radiation shift assessment for a lutetium ion clock”. Nat. Comm., 9:1650, 2018.
[4] R. Kaewuam, et al, “Hyperfine averaging by dynamic decoupling in a multi-ion lutetium clock”. Phys. Rev Lett. 124, 083202, 2020.
[5] T. R. Tan, et al, “Suppressing inhomogeneous broadening in a lutetium multi-ion optical clock”. Phys. Rev. Lett. 123 063201, 2019.
[6] R. Kaewuam, et al, “Laser Spectroscopy of 176Lu+”. J. Mod. Opt. 65 592-60, 2017.
[7] K. J. Arnold, et al, “Polarizability assessments of ion-based optical clocks”. Phys. Rev. A 100 043418, 2019.
[8] S.R. Chanu, et al, “Magic wavelength of the 138Ba+ 6s 2S1/2 − 5d 2D5/2 clock transition”. Phys. Rev. A 101 042507, 2020.
[9] Z. Zhang, et al, “Hyperfine-mediated effects in a Lu+ optical clock”. Phys. Rev. A 102 052834, 2020.
[10] R. Kaewuam, et al, “Precision measurement of the 3D1 and 3D2 quadrupole moments in Lu+”. Phys. Rev. A 102 042819, 2020.
