Speakers
Description
The $^{229}$Th nucleus has the unique property of a very low-lying isomeric first excited state with an excitation energy of only 8.338(24) eV [1], which is addressable with state-of-the-art VUV frequency comb laser systems. Storage in the isolated environment of a cryogenic ion trap will allow for lifetime measurements of the excited isomeric state (expected in the range of a few 10$^3$ seconds), precise spectroscopy of the nuclear transition, and eventually the creation of the first nuclear clock with an estimated systematical uncertainty approaching 10$^{-19}$ [2].
For loading of $^{229}$Th$^{3+}$ ions into the ion trap, a compact version of the very successful He-buffer-gas-cell ion source used in [3-5] has been designed, built, and commissioned at LMU. The compactness of the setup will allow the installation on the laser table next to the ion trap where $^{229}$Th$^{3+}$ will be trapped and sympathetically cooled by laser-cooled $^{88}$Sr$^+$ ions. The challenging boundary conditions of 32 mbar He in the buffer gas cell and $<10^{-8}$ mbar in the ion trap require several stages of differential pumping, which have been implemented.
In this contribution, we report on the commissioning of the compact He-buffer-gas-cell ion source, including the demonstration of the fulfilment of the differential pumping requirements, and first experiments towards transferring $^{229}$Th$^{3+}$ to and trapping of $^{229}$Th$^{3+}$ in the ion trap. In addition, we report on efforts to integrate an ablation ion source for $^{88}$Sr$^+$ into the ion guide between the buffer gas cell and the ion trap for combined extraction of $^{229}$Th$^{3+}$ and $^{88}$Sr$^+$.
This work was supported by the European Research Council (ERC grant agreement No. 856415) and BaCaTec (7-2019-2).
[1] S. Kraemer et al., Observation of the radiative decay of the $^{229}$Th nuclear clock isomer, Nature 617, 706–710 (2023).
[2] C. Campbell et al., Single-ion nuclear clock for metrology at the 19th decimal place, Phys. Rev. Lett. 108, 120802 (2012).
[3] L. von der Wense et al., Direct detection of the $^{229}$Th nuclear clock transition, Nature 533, 47–51 (2016).
[4] B. Seiferle et al., Lifetime Measurement of the $^{229}$Th Nuclear Isomer, Phys. Rev. Lett. 118, 042501 (2017).
[5] B. Seiferle et al., Energy of the $^{229}$Th nuclear clock transition, Nature 573, 243–246 (2019).
