Trapping and sympathetic cooling of single thorium ions for spectroscopy

Abstract

Precision optical spectroscopy of exotic ions reveals accurate information about nuclear properties such as charge radii and magnetic and quadrupole moments. Thorium ions exhibit unique nuclear properties with high relevance for testing symmetries of nature. We report loading and trapping of single ${}^{232}$Th${}^{+}$ ions in a linear Paul trap, embedded into and sympathetically cooled by small crystals of trapped ${}^{40}$Ca${}^{+}$ ions. Trapped Th ions are identified in a non-destructive manner from the voids in the laser-induced Ca fluorescence pattern emitted by the crystal, and alternatively, by means of a time-of-flight signal when extracting ions from the Paul trap and steering them into an external detector. We have loaded and handled a total of 231 individual Th ions. We reach a time-of-flight detection efficiency of $\gtrsim 95\%$, consistent with the quantum efficiency of the detector. The sympathetic cooling technique is expected to be applicable for other isotopes and various charge states of Th e.g., for future studies of ${}^{229m}$Th.

arXiv comment5 pages, 4 figures

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• Concepts for direct frequency-comb spectroscopy of ${}^{229\text{m}}$Th and an internal-conversion-based solid-state nuclear clock
• Exotic Bohmian arrival times of spin-1/2 particles I-An analytical treatment
• Fabrication of ${}^{15}{\text{NV}}^{-}$ centers in diamond using a deterministic single ion implanter
• Sympathetic cooling of trapped Th3+ alpha-recoil ions for laser spectroscopy
• Alpha spectrometric characterization of thin ${}^{233}$U sources for ${}^{229\text{(m)}}$Th production
• Catching, trapping and in-situ-identification of thorium ions inside Coulomb crystals of ${}^{40}$Ca${}^{+}$ ions
• Robust Polarization Gradient Cooling of Trapped Ions
• Development of a recoil ion source providing slow Th ions including ${}^{229(m)}$Th in a broad charge state distribution
• Studies of thorium and ytterbium ion trap loading from laser ablation for gravity monitoring with nuclear clocks
• Fluorescence calorimetry of an ion crystal
• Laser fluence-dependent production of molecular thorium ions in different charge states for trapped-ion experiments
• Formation of Two-Ion Crystals by Injection from a Paul-Trap Source into a High-Magnetic-Field Penning Trap