sohkamyung, Cool. Positronium 'atoms' are made up of an electron and a positron.
"Researchers are [...] actively seeking tricks to make sources of positronium atoms that live longer. In a paper published today in the journal Physical Review A, the AEgIS collaboration at CERN describes a new way of making long-lived positronium."
https://home.cern/news/news/physics/aegis-makes-positronium-antimatter-gravity-experiments