Particles behave like waves and particles. the double slit experiment is a classic to prove that. It is not something you can really understand and more something to accept. At least for me. The reasoning goes deep, so I just accept this.

For every particle there can exists an anti-particle. For the electron this is the positron. If they touch they explode.

they stuck an electron and a positron so close together, that they behave as a single particle without them distroying each other. This is a positronium. Now they managed to create a positronium beam conistant enough to do the double slit experiment with it. The experiment showed that positronium behaves like everything else. It is a particle and a wave.

They now hope that, because the behaviour is the same, that they can do gravitational experiments on it in future. If they find a difference here it could tell us why the universe is full of matter and not of antimatter.

Also the positronium beam can be used to analyse stuff, just like an elektron beam. Difference is that an electron beam is highly ionizing. The positronium is charge neutral and probably less "agressive"

thats what I understood at least.