Motivation:

For the measurement of the g-factor of the electron to an accuracy of 2.8 x 10-13 and for low energy antimatter physics, which included sensitive probes of the baryon/antibaryon asymetry and whose pioneering methods opened the way to antihydrogen production and future spectroscopy.
In particular, his measurement of the dimensionless electron magnetic moment, the electron g-value, is 15 times more accurate than the measurement performed by Hans Dehmelt twenty years earlier. Such precision opens the way to QED tests of unprecedented accuracy and allows the testing of possible finite size and composite structure of the electron, not yet detected. In addition, Gerald Gabrielse was the first to propose the use of low-energy antiprotons and methods to produce cold antihydrogen atoms that could be trapped for spectroscopic analyses. In 2002, two teams (one led by Gabrielse) produced antihydrogen during the positron cooling of antiprotons within a nested Penning trap – a method and device that Gabrielse had invented.

(reproduced from the Tomassoni Prize website)