

The particle does not have to interact directly with matter to be observable.
Apparently they built what they called a “one-positron quantum cyclotron”, meaning they made their single positron “fly in a circle” with magnetic fields to trap it.
That way you have a moving charge, which you can manipulate with electromagnetic radiation, microwaves in this case, the same way as you could with normal matter. That also means you can make your particle emit electromegnetic radiation that will tell you it is still there without touching anything.
Still kind of mindblowing, that they can reliably detect anything coming from a single positron though.






Neat, this seems very similar in concept to how the difference between fluorescence and phosphorescence is usually explained. They just observed it with electron-hole recombination instead of light emission.
So, not an entirely unknown concept, but in a field of material research it has not been seen before. Sounds like a solid basis to go looking for new materials for photovoltaics, now that we know what to look for in candidates.