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$J$ = 0 metastable state of ${Th}^{2 +}$ for a hyperfine-free nuclear clock

S. Sagar Maurya , V. Lal , J. Tiedau , M. V. Okhapkin , and E. Peik ^*

Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany

^*Contact author: ekkehard.peik@ptb.de

Phys. Rev. A 114, 032819 – Published 17 September, 2026

DOI: https://doi.org/10.1103/c98g-6f84

Abstract

We present measurements on a metastable state in ${Th}^{2 +}$ with the electronic configuration $6 d^{2} {}^{3}P_{0} (5090 {cm}^{- 1})$ . This is motivated by the prospect of using the state in laser excitation of the low-energy ${}^{229}{Th}$ nuclear resonance independent from the leading hyperfine interactions. The $6 d^{2} {}^{3}P_{0}$ state has no dipole-allowed radiative decay channel and is connected to the second ground state $6 d^{2}^{3} F_{2} (63 {cm}^{- 1})$ through an electric quadrupole transition only. We populate the state by laser excitation at 484 nm via a higher excited level and detect its population in laser-induced fluorescence. The isotope shift of the $J = 0$ level between ${}^{232}{Th}^{2 +}$ and ${}^{229}{Th}^{2 +}$ is determined as a measure of the interaction of electronic and nuclear charge distributions. The lifetime of the level in our ion trap with buffer gas is limited by collisional mixing with the nearby state $5 f 6 d {}^{3}G_{3} (5060 {cm}^{- 1})$ . In ultrahigh vacuum, it could serve as a hyperfine-free nuclear clock that is largely immune to field-induced frequency shifts via the electron shell.

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Phys. Rev. A 114, 032819– Published 17 September, 2026

Vol. 114, Iss. 3 — September 2026

Received 7 May 2026
Accepted 1 September 2026

DOI: https://doi.org/10.1103/c98g-6f84

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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$J$ = 0 metastable state of ${Th}^{2 +}$ for a hyperfine-free nuclear clock

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J = 0 metastable state of Th2+ for a hyperfine-free nuclear clock

Abstract

Physics Subject Headings (PhySH)

Article Text

References (53)

$J$ = 0 metastable state of ${Th}^{2 +}$ for a hyperfine-free nuclear clock