We investigate fundamental properties and interactions of light exotic systems, especially muonic atoms such as µH and µD or muonic ions such as µHe⁺, µLi⁺⁺ and µBe³⁺, by means of laser spectroscopy. The studies include i.a. tests of bound-state quantum electrodynamics, measurements of nuclear electric and magnetic charge radii, improved determination of the Rydberg constant and tests of few-nucleon models. Our activities cover a large range of interesting fields in nuclear, atomic, and particle physics, ranging from laser spectroscopy in neutral atom traps and  ion traps, particle accelerators to the fundamental building blocks in nature.


Muonic Beryllium
We aim to stop muons in a penning trap filled with beryllium ions. In this process muonic beryllium ions (bound state of a bare Be⁴⁺ nucleus and a single negative muon) are formed which can be used to test bound state QED and to precisely measure nuclear properties and set benchmarks for few-nucleon models. This experiment is a fundamental step towards precise nuclear charge radius determinations of non-gaseous low-Z elements.
In the Triton-Radius EXperiment we will first trap atomic hydrogen and perform high-precision laser spectroscopy on it. In a second stage this will be done with Tritium. This experiment will be used to test bound state QED and to measure nuclear properties of Tritium.
Cold atoms are a versatile tool for studying fundamental interactions and neutral-neutral collisions. We use magneto-optically trapped lithium atoms to perform high-precision laser spectroscopy to access fundamental nuclear properties. In addition, the lithium MOT serves as a cold target for stopping atomic beams.
1S HFS measurements in muonic hydrogen and helium-3
The measurement of the ground-state hyperfine splitting (1S-HFS) in muonic hydrogen and helium-3 gives insight about the nuclear polarizability and magnetic properties of the nucleus which are parametrized with the Zemach radius. The Zemach radius is a convolution of the electric and the magnetic charge distribution. The 1S-HFS measurements are therefore a complementary way to the nuclear magnetic radius compared to electron scattering experiments.

Lamb shift measurements in muonic hydrogen, deuterium and helium-3/-4
We measure the 2S-2P energy difference (Lamb shift) in muonic hydrogen and deuterium atoms as well as in muonic helium-3 and -4 ions. These measurements allow us to precisely determine the nuclear charge radii of these atoms and to improve the determination of the Rydberg constant. The Lamb shift measurement is therefore a test of bound-state quantum electrodynamics (QED) and additionally gives insight about the nuclear polarizability and other nuclear properties. The measurement in muonic hydrogen has raised the so-called proton radius puzzle.