Positronium is a short-lived pairing of an electron and its antimatter counterpart, the positron. For decades, physicists had confirmed that plenty of things behave like waves under the right conditions, electrons, neutrons, even whole helium atoms and molecules. Positronium, though, had never been caught doing it. Until now.
According to a paper published in Nature Communications, researchers fired a carefully tuned positronium beam through a sheet of graphene and watched what came out the other side. Using time-of-flight selection paired with spatially resolved detection, they picked out a distinct first-order diffraction peak, and it landed exactly where matter-wave predictions said it should. That single peak is the tell: it’s the signature of diffraction, the same phenomenon that shows up when light or particles bend around obstacles and interfere with themselves.
What makes this result count as definitive, per the study, is what it rules out. The diffraction pattern confirms that positronium was interfering as one coherent quantum entity, not as two separate particles just happening to overlap. Small distinction on paper, huge one in practice: it means this antimatter system followed the same wave-particle rulebook physicists have long verified in ordinary matter, closing a gap that had stood open for a surprisingly long time.