Rostock 2019 – scientific programme

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A: Fachverband Atomphysik

A 35: Precision Spectroscopy of atoms and ions

A 35.12: Poster

Thursday, March 14, 2019, 16:15–18:15, S Fobau Physik

Approaching sympathetic cooling of trapped ²²⁹Th³⁺ ions — •Gregor Zitzer, Johannes Thielking, David-Marcel Meier, Maksim Okhapkin, and Ekkehard Peik — Physikalisch-Technische Bundesanstalt, Braunschweig, Germany

With only a few eV above its nuclear ground state the isomer of ²²⁹Th is accessible for direct laser excitation. The isomeric transition may be used as a frequency reference for a new type of optical clocks which is exceptionally insensitive to field-induced frequency shifts.

For the realization of an optical nuclear clock with laser-cooled trapped ions the charge state 3+ of ²²⁹Th is preferred, due to its relatively simple and convenient electronic level structure. Direct laser cooling of ²²⁹Th³⁺ and ²³²Th³⁺ has been demonstrated [1,2].

Due to limitations in the reachable laser cooling power we plan to investigate sympathetic cooling of ²²⁹Th³⁺ with ⁸⁸Sr⁺ for experiments with large Coulomb crystals and a future clock operation. In a new setup ²²⁹Th³⁺ and ⁸⁸Sr⁺ will be trapped in a linear radiofrequency ion trap. It is planed to extract the ²²⁹Th³⁺ ions generated by a ²³³U source via α-decay [3] and guide them to a segmented linear Paul trap. In this trap the laser cooled ⁸⁸Sr⁺ ions will surround the ²²⁹Th³⁺ forming a prolate spheroid. Here the concept, design and current status of the experiment on ²²⁹Th³⁺ will be shown.

[1] C. J. Campbell et al., Phys. Rev. Lett. 102, 233004 (2009)

[2] C. J. Campbell et al., Phys. Rev. Lett. 106, 223001 (2011)

[3] L. v. d. Wense, On the direct detection of ^229mTh, Springer International Publ., DOI: 10.1007/978-3-319-70461-6 (2018)