Progress Towards Transport and Neutralization of Fr⁺ ions for Magneto-Optical Trapping of Fr atoms

We are developing continuous, offline sources to produce Fr⁺ ions at few-keV energies, fed from the radioactive decay of long-lived ²²⁹Th. These ions will be embedded into a low work function metal foil, which acts to neutralize the ions. Heating the foil will release Fr atoms into a vapor cell with an anti-stick coating for efficient loading into a magneto-optical trap (MOT). This poster describes our development of systems for neutralizing and trapping Fr atoms, as well as ion optics for transport of Fr⁺ ions. Our work follows that of several established techniques [1, 2]. We perform initial optimization of the system using Rb⁺ ions and Rb atoms, which act as stable surrogates with relevant properties similar to those of Fr. The Fr MOT is key to an experiment (REDRUM) that aims to create ultracold FrAg molecules to detect the CP-violating Schiff moment of the ²²¹Fr nucleus. The static octupole deformation of the ²²¹Fr nucleus [3] and the highly ionic FrAg molecules [4, 5] will offer unprecedented sensitivity to new sources of hadronic CP-violation at the 100 TeV scale. We present our characterization of Rb/Fr⁺ neutralization and release efficiency, as well as residence times and trap collection efficiency for atoms in the MOT. We also describe developments in ion optics for transporting the Fr⁺ beam. These systems represent a key step towards routine production of Fr MOTs in a university laboratory.

[1] G Gwinner and L A Orozco. Studies of the weak interaction in atomic systems: towards measurements of atomic parity non-conservation in francium.

Quantum Science and Technology, 7(2):024001, Jan 2022.

[2] Z.-T. Lu, K. L. Corwin, K. R. Vogel, C. E. Wieman, T. P. Dinneen, J. Maddi, and Harvey Gould. Efficient collection of 221fr into a vapor cell magneto-optical trap. Phys. Rev. Lett., 79:994–997, Aug 1997.

[3] V. V. Flambaum and A. J. Mansour. Enhanced nuclear Schiff and electric dipole moments in nuclei with octupole deformation. Phys. Rev. C, 111:055501, May 2025.

[4] Aurlien Marc, Mickael Hubert, and Timo Fleig. Candidate molecules for next-generation searches of hadronic charge-parity violation. Phys. Rev. A, 108:062815, Dec 2023.

[5] Jacek Kłos, Hui Li, Eite Tiesinga, and Svetlana Kotochigova. Prospects for assembling ultracold radioactive molecules from laser-cooled atoms. New Journal of Physics, 24(2):025005, Feb 2022.