Timo Dickel

Linear radio-frequency quadrupole (RFQ) traps are crucial for ion and phase-space manipulation across diverse physics platforms, including quantum information processing, precision atomic spectroscopy, and high-resolution mass or laser spectrometry. We present the design, electrostatic field optimization, and performance characterization of a scalable, multi-layer printed circuit board (PCB) linear RFQ trap. By utilizing a PCB-based "stacked-electrode" geometry to generate high-quality quadrupolar fields, this architecture suppresses higher-order multipole field components by up to an order of magnitude compared to planar "flat surface-electrode" designs and allows for reclaiming up to 60% of the radial pseudopotential-well depth of an ideal hyperbolic quadrupole. Following a thorough optimisation and characterization using both simulations and experiments, we demonstrate its suitability as a cooler buncher, showing rapid helium buffer-gas cooling with time constants between 34 +/- 3 us and 412 +/- 23 us, and achieving a highly compressed longitudinal phase-space emittance of only 58 +/- 4 eV*ns. The low beam emittance provides flexible control of the extracted bunch properties: weak extraction fields yield energy spreads down to 2.5 +/- 0.4 eV, whereas strong fields produce ultra-narrow temporal widths down to 2.6 +/- 0.3 ns. The results establish our PCB-RFQ platform as a versatile, scalable, and cost-effective alternative to traditionally machined rod-based RFQ assemblies for advanced ion-trapping, beam-preparation, or quantum applications.

Molecules have proven to be sensitive tools for studying physics beyond the standard model, with heavy and deformed nuclei offering decisive sensitivity to parity- and time-reversal-violating effects. However, almost all elements beyond lead, occupying the 6p~to~5f atomic orbitals, lack stable isotopes, hence molecules containing them are referred to as radioactive molecules. Among those, radium monofluoride has seen particular interest, but to date, research on radioactive molecules has mainly been limited to large-scale nuclear facilities. Here, we present a scheme that allows efficient and fast harvest of radioactive ions (including short-lived Ra), and show ion gas-phase reaction studies of singly and doubly charged Ra, Po, and Pb ions with SF$_6$ gas inside an ion trap. Our results show that the chemical reaction rate of Ra$^+$ is in line with trends of other alkaline earth elements, further support by quantum chemical computations. The reaction Ra$^{2+}$ + SF$_6$ $\rightarrow$ RaF${^+}$ + SF$_5^{+}$ achieves an almost unity conversion efficiency, making it particularly suitable for the application for studies in physics beyond the standard model. The scheme enables future decentralized research avenues with short-lived radioactive molecules for fundamental physics research at laboratories without the need for local nuclear reactors or accelerators.

While laser excitation of the nuclear isomeric transition in $^{229}$Th has been recently achieved for thorium atoms embedded in large-bandgap crystals, laser excitation and characterization of the nuclear transition in trapped $^{229}$Th$^{3+}$ ions has not yet been accomplished. To address these experiments, a cryogenic Paul trap setup has been designed, built, and commissioned at LMU Munich. Here, we present the specifications of the new experimental platform and demonstrate its successful operation, showing the extraction, subsequent ion-guiding, mass-purification, and trapping of $^{229}$Th$^{3+}$ and $^{229\text{m}}$Th$^{3+}$ ions from a newly designed buffer-gas stopping cell as well as of $^{88}$Sr$^{+}$ ions from laser ablation of a solid target. Further, we show sympathetic laser cooling of $^{229\text{(m)}}$Th$^{3+}$ by Doppler-cooled $^{88}$Sr$^{+}$ ions and the formation of mixed-species Coulomb crystals.

High-precision mass measurements of exotic $^{95-97}$Ag isotopes close to the $N = Z$ line have been conducted with the JYFLTRAP double Penning trap mass spectrometer, with the silver ions produced using the recently commissioned inductively-heated hot cavity catcher laser ion source at the Ion Guide Isotope Separator On-Line facility. The atomic mass of $^{95}$Ag was directly determined for the first time. In addition, the atomic masses of $β$-decaying 2$^+$ and 8$^+$ states in $^{96}$Ag have been identified and measured for the first time, and the precision of the $^{97}$Ag mass has been improved. The newly measured masses, with a precision of $\approx$ 1 keV/c$^2$, have been used to investigate the $N =$ 50 neutron shell closure confirming it to be robust. Empirical shell-gap and pairing energies determined with the new ground-state mass data are compared with the state-of-the-art \textit{ab initio} calculations with various chiral effective field theory Hamiltonians. The precise determination of the excitation energy of the $^{96m}$Ag isomer in particular serves as a benchmark for \textit{ab initio} predictions of nuclear properties beyond the ground state, specifically for odd-odd nuclei situated in proximity to the proton dripline below $^{100}$Sn. In addition, density functional theory (DFT) calculations and configuration-interaction shell-model (CISM) calculations are compared with the experimental results. All theoretical approaches face challenges to reproduce the trend of nuclear ground-state properties in the silver isotopic chain across the $N =$50 neutron shell and toward the proton drip-line.

A novel method for simultaneous measurement of masses, Q-values, isomer excitation energies, half-lives and decay branching ratios of exotic nuclei has been demonstrated. The method includes first use of a stopping cell as an ion trap, combining containment of precursors and decay-recoils for variable durations in a cryogenic stopping cell (CSC), and afterwards the identification and counting of them by a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). Feasibility has been established by recording the decay and growth of $^{216}$Po and $^{212}$Pb (alpha decay) and of $^{119m2}$Sb (t$_{1/2}$ = 850$\pm$90 ms) and $^{119g}$Sb (isomer transition), obtaining half-lives and branching ratios consistent with literature values. Hardly any non-nuclear-decay losses have been observed in the CSC for up to $\sim$10 seconds, which exhibits its extraordinary cleanliness. For $^{119}$Sb, this is the first direct measurement of the ground and second isomeric state masses, resolving the discrepancies in previous excitation energy data. These results pave the way for the measurement of branching ratios of exotic nuclei with multiple decay channels.