Radio-frequency induced spin transitions of one individual proton are observed for the first time. The spin quantum jumps are detected via the continuous Stern-Gerlach effect, which is used in an experiment with a single proton stored in a cryogenic Penning trap. This is an important milestone towards a direct high-precision measurement of the magnetic moment of the proton and a new test of the matter-antimatter symmetry in the baryon sector.
@article{arxiv.1104.1206,
title = {Observation of Spin Flips with a Single Trapped Proton},
author = {S. Ulmer and C. C. Rodegheri and K. Blaum and H. Kracke and A. Mooser and W. Quint and J. Walz},
journal= {arXiv preprint arXiv:1104.1206},
year = {2015}
}