Laser Spectroscopy of Electronic Transitions of the Nuclear Clock Isomer 229mth3+ in a Cryogenic Paul TrapHYBRID

The Th^-229 nucleus has the unique property of an extremely low lying isomeric first excited state. 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 200 s, the isomeric state can be directly excited with laser light from state-of-the-art VUV laser systems. Consequently, Th^-229 is the ideal candidate for a nuclear optical clock.

Furthermore, due to a near-cancellation between the large Coulomb energies of ground and isomeric state as part of the nuclear binding energy, the nuclear clock transition has an about three orders of magnitude larger sensitivity to potential and theoretically predicted time variation of the fine structure constant compared to electronic transitions in other atoms.

While the isomeric state was recently directly excited with laser light for Th^-229 ions embedded in CaF₂ and other solid-state crystals, the nuclear clock project at LMU focusses on the trapped ion approach with laser-cooled ²²⁹Th^3+, which features suitable electronic transitions for fast nuclear state readout and extremely low systematic uncertainties.

This talk will present the status of the experiment at LMU with an emphasis on trapping and sympathetic laser-cooling of ^229mTh³⁺ ions embedded in mixed-species ^229mTh³⁺/⁸⁸Sr⁺ Coulomb crystals, and will report on ongoing laser spectroscopy of the electronic transitions in ^229mTh³⁺.

https://gsi-fair.zoom.us/j/63856816325
Meeting-ID: 638 5681 6325
Passcode: AP_Seminar
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