A team of researchers at a Microsoft laboratory in the Netherlands, who published a 2018 paper in the journal Nature, has now retracted that paper, citing a lack of evidence to support their previous conclusions. The study involved trying to prove the existence of the fermion—a theorized particle that could possibly be both matter and antimatter. The retraction came after Sergey Frolov, a researcher at the University of Pittsburgh in Pennsylvania, found that another quantum phenomenon could mimic the results found by the original research team. After a re-analysis of their work, the researchers agreed with Frolov and contacted Nature to ask for a retraction.