Observation experiment of resonance transition of positronium hyperfine structure in static periodic magnetic field

The resonant excitation of atoms is usually induced by electromagnetic waves such as lasers and microwaves, but it can also be induced by static field with a spatially periodic structure (here called as static periodic field). When atoms moving in a static periodic field feel a temporally oscillating field in the center of gravity system, and its frequency matches the transition frequency of the atoms, resonant transition occurs. Recently, as a new attempt of this technique, resonant transitions in positronium as the hyperfine structure of exotic atom have been experimentally observed. This commentary plainly introduces the significance of this study, experimental method, and details of results. (A.O.)