 Gabrielse now leads the ATRAP team at CERN, one of the two teams that first produced slow antihydrogen atoms and suspended them in a magnetic trap.Both TRAP and ATRAP teams used trapped antiprotons within a nested Penning trap device to produce antihydrogen atoms slow enough to be trapped in a magnetic trap.The team made the first one-particle comparison of the magnetic moments of a single proton and a single antiproton.