“We have a common goal: We want to use the isotope Thorium-229 to test the standard model of Particle Physics. In the TACTICa project, we work hand in hand with our co-workers from experimental atomic physics. The name TACTICa (Trapped And Cooled Thorium Ion spectroscopy via Calcium) says it all: We trap individual Thorium-229 ions in a special ion trap in order to be able to examine them using laser spectroscopy. To do this, we must first slow down the thorium ions – or cool them, as we say. Calcium, which is also on board, helps us with this. We call this method quantum logic spectroscopy: We actually want to find out something about the thorium, but in order to manipulate it, we need calcium as a helper, as a logic ion.”

What makes Thorium-229 so special? With the metastable state Thorium-229m, it possesses by far the lowest excited energy level of all currently known approximately 3,800 atomic nuclei. It is therefore the only nuclear transition that can potentially be interrogated with lasers. The extremely precise measurement of this transition and the two nuclear states opens up exciting perspectives. In particular, thorium becomes a test laboratory for new physics for us. For example, we want to answer the question of whether certain natural constants might not be so constant after all, but change with time or location. In turn, some theories on dark matter that go beyond the standard model predict this.

We are currently working in nuclear chemistry to produce suitable uranium-233 sources and to direct the Thorium-229 daughters from the radioactive decay of the uranium into our trap – while from the theoretical side we are developing models for what the smallest deviations between measured and expected results can reveal about new physics. We have already been able to show that the method works in principle.”

Dr. Raphael Haas is a nuclear chemist in the group of Prof. Dr. Christoph Düllmann, Anna Viatkina studied in Russia and works as a theoretical physicist in the group of Prof. Dr. Dmitry Budker on her doctoral thesis. The TACTICa project is funded as part of a “Helmholtz Excellence Network” in the area of “Matter and Universe.”