Mainz 2026 – wissenschaftliches Programm
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Q: Fachverband Quantenoptik und Photonik
Q 13: Nuclear Clocks
Q 13.4: Vortrag
Montag, 2. März 2026, 17:45–18:00, P 11
A cryogenic Paul trap for spectroscopy of the nuclear clock isomer 229mTh3+ — •Markus Wiesinger, Georg Holthoff, Kevin Scharl, Tamila Teschler, Daniel Moritz, and Peter G. Thirolf — Ludwig-Maximilians-Universität München
The 229Th nucleus has the unique property of an extremely low lying isomeric first excited state (denoted 229mTh). With an excitation energy of 8.356 eV – corresponding to a wavelength of 148.4 nm – and an expected lifetime of the ionic thorium isomer in vacuum of about 2000 s, the isomeric state can be directly excited with laser light from state-of-the-art VUV laser systems. Consequently, 229Th is the ideal candidate for a nuclear optical clock. Furthermore, the nuclear clock transition has an about 103 times larger sensitivity to time variation of the fine structure constant compared to transitions in other atoms.
While the isomeric state was recently directly excited with laser light in 229Th doped CaF2 and other solid-state crystals, the nuclear clock project at LMU focusses on the trapped ion approach with laser-cooled 229Th3+, which features suitable electronic transitions for fast nuclear state readout and extremely low systematic uncertainties.
This talk will give an overview of the cryogenic Paul trap apparatus routinely applied for sympathetic laser-cooling of 229(m)Th3+ ions embedded in mixed-species 229(m)Th3+/88Sr+ Coulomb crystals. We will show simultaneous fluorescence imaging of trapped 88Sr+ ions at 422 nm and 229Th3+ ions at 690 nm using two cameras, laying the foundations for measuring the lifetime of 229mTh3+ in vacuum and for quantum state readout after VUV excitation of the nuclear transition.
Keywords: Nuclear Clock; Trapped Ions; Sympathetic Laser Cooling; Laser Spectroscopy; Thorium-229