Ulmer Initiative Research Unit

Our main research interest focuses on high-precision studies of simple antimatter systems. We are developing an experiment for the ultra-high precision determination of the magnetic moment of the proton and the antiproton. The magnetic moment of the antiproton is currently known at a level of only 10-3. We are aiming at a millionfold improved measurement of this fundamental quantity. To this end we construct a new apparatus, where a single antiproton will be stored in a cryogenic double Penning trap for arbitrarily long time. Performing quantum-jump spectroscopy by application of the continuous Stern-Gerlach effect, the magnetic moment of the particle can be determined with high precision. Recently we observed spin flips with a single trapped proton, and based on these measurements the magnetic moment was determined with a relative precision of 8*10-6. Thus, applying our technique to the antiproton would improve the number by more than two orders of magnitude. Experimental efforts for an improvement of our technique towards 10-9 are under way. To this end we are involved as well in the proton g-factor experiment which is operated at the University of Mainz, in collaboration with Max Planck Institute for Nuclear Research at Heidelberg and GSI Darmstadt.

In addition our research unit contributes to the ASACUSA-MUSASHI collaboration, which is working on the production of a polarized antihydrogen beam using a so-called CUSP trap. The polarized beam will be used to investigate the anithydrogen hyperfine structure with high precision.Together with a high precision mesurement of the magnetic moment of the proton, from these data constraints on the substructure of the antiproton are obtained.

Furthermore we develop highly sensitive detection systems and cryogenic low noise electronics to several storage ring and Penning trap experiments.


  • High precision measurement of the magnetic moment of the proton and the antiproton.
  • Precision measurement of the antihydrogen hyperfine structure.
  • Development of novel techniques for high-precision Penning trap experiments.
  • Pick-up systems and low-noise electronics.


Fundamental physics, CPT symmetry, Magnetic moments, Antiprotons, Penning traps, pick-up systems, cryogenic electronics.

Stefan Ulmer

Team Leader: Stefan Ulmer