We just published a review article which gives detailed insight into the proton g-factor experiment at Mainz. The article contains as well a low resolution measurement of the proton magnetic moment it a fractional precision of 8.9 ppm.
Penning traps are extremely powerful and versatile tools for high precision physics. This enormous impact is mainly based on the fact that in the magnetic field B of the trap the free cyclotron frequency of a trapped particle can be measured with high fractional precision. We invented a novel method to measure the free cyclotron frequency of a single trapped proton in one shot. The method is based on double-dressed states. By application of frequency modulated sideband drives the double dressing is produced, and energy is transferred between all eigenmodes of the trapped particle.
We have observed spin quantum-jumps with a single trapped proton for the first time. The result is a pioneering step forward in the endeavor to directly measure the magnetic properties of the proton and the antiproton with high precision, and was just published in Physical Review Letters. The measuring principle is based on the observation of a single proton stored in a Penning trap.