Stefan Ulmer (born 1977 in
Tübingen) is a
particle physicist, professor of Physics at
Heinrich Heine University Düsseldorf and chief scientist at the Ulmer Fundamental Symmetries Laboratory,
RIKEN, Tokyo. He is the founder and the spokesperson of the
BASE experiment (AD-8) at the
Antiproton Decelerator facility at
CERN, Geneva. Stefan Ulmer is well known for his contributions to improving
Penning trap techniques and precision measurements on
antimatter. He is the first person to observe spin transitions with a single trapped proton as well as single spin transitions with a single trapped
antiproton, a significant achievement towards a precision measurement of the antiproton
magnetic moment.[1][2][3]
After his Ph.D. studies, Stefan Ulmer joined the
ASACUSA CUSP experiment at CERN in 2012 as a
postdoctorate fellow, and contributed to the production of the first polarized beam of
antihydrogen atoms.[6][5] Simultaneously, he worked on setting up the
BASE experiment. He invented a reservoir trap technique that allowed BASE to store antiprotons for about 400 days.[7] In 2014, Stefan Ulmer’s team performed the most precise measurement of the proton-antiproton
charge-to-mass ratio, evidently the most accurate test of
CPT invariance of
baryons.[1][3][8] In 2017, his team reported the first observation of single antiproton
spin transitions,[9] and also completed the most precise measurements of antiproton
magnetic moment.[10] From a time-base analysis of these data the most stringent limits on
dark-matter / antimatter coupling were derived.[11] Inspired by this work, the BASE collaboration has used Penning trap detection systems as axion haloscopes, to set competitive limits on axion-to-photon conversion.[12] In 2022 Ulmer's team reported on a comparison of the proton/antiproton charge-to-mass ratio with a fractional accuracy of 16 parts in a trillion.[13] This measurement also constitutes the first differential test of the clock
weak equivalence principle with antiprotons. Ulmer's measurements are considered to be outstanding and of great value for fundamental physics research.[1][3][14]
Awards and recognition
Stefan Ulmer has received the following awards and recognition for his contributions to fundamental experimental physics.
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