ALPHA (Antihydrogen Laser Physics Apparatus) is an international collaboration based at CERN, and which is working with trapped antihydrogen atoms, the antimatter counterpart of the simplest atom, hydrogen. By precise comparisons of hydrogen and antihydrogen, the experiment hopes to study fundamental symmetries between matter and antimatter.
Once you've trapped antihydrogen what do you do? You measure it!
We report the first resonant quantum transitions in antihydrogen atoms.