TACTICa: Trapped And Cooled Thorium Ion spectroscopy via Calcium

Principal Investigators:

D. Budker (Helmholtz Institute Mainz, PRISMA+ Cluster of Excellence, and the JGU QUANTUM group),
Ch.E. Düllmann (Helmholtz Institute Mainz, PRISMA+ Cluster of Excellence and Institute of Nuclear Chemistry, JGU Mainz, GSI Helmholtzzentrum für Schwerionenforschung Darmstadt)
F. Schmidt-Kaler (Helmholtz Institute Mainz, JGU, Institute for Physics, PRISMA+ Cluster of Excellence)


TACTICa uses atomic physics methods to investigate thorium isotopes including the metastable low energy nuclear state in 229mTh. The optical ground state transition of isomeric 229Th is the only nuclear transition that potentially can be interrogated using lasers. Controlling this transition opens an interesting window into high-precision tests of the standard model and on possible variation of fundamental constants.
Thus TACTICa aims to deploy ion trapping techniques like quantum logic spectroscopy to gain access to the nuclear structure of thorium.

TACTICa aims for combining unique expertise of nuclear chemistry and experimental quantum science. This way, we will first vastly improve the accuracy of spectroscopic investigations of the nuclear Th isotopes including the isomer in 229Th, and eventually realize quantum logic spectroscopy and quantum-enhanced measurements on thorium for fundamental research.



As an important first demonstration, in 2018, single 232Th+ ions were trapped together with Ca+ ions forming a so-called “Wigner cryscal”, sympathetically cooled and characterized.

The ions were successfully trapped in a linear Paul trap, and their mass was identified via a time-of-flight (TOF) measurement as well as from the voids in the laser-induced Ca+ fluorescence pattern emitted by the Wigner crystal. This paves the way to future high-precision studies of various Th isotopes including 229mTh in the context of fundamental physics or quantum optics. 



Karin Groot-Berning, Felix Stopp, Georg Jacob, Dmitry Budker, Raphael Haas, Dennis Renisch, Jörg Runke, Petra Thörle-Pospiech, Christoph Düllmann, and Ferdinand Schmidt-Kaler,
Trapping and sympathetic cooling of single thorium ions for spectroscopy
Phys. Rev. A 99, 023420 (2019); arXiv:1807.05975


Felix Stopp, Karin Groot-Berning, Georg Jacob, Dmitry Budker, Raphael Haas, Dennis Renisch, Jörg Runke, Petra Thörle-Pospiech, Christoph E. Düllmann, Ferdinand Schmidt-Kaler,
Catching, trapping and in-situ-identification of thorium ions inside Coulomb crystals of 40Ca+ ions,
Hyp. Int. 240, 33 (2019)