What breaks quantum monogamy? Electron crowding delivers a surprise

New research challenges the long-held notion of quantum monogamy, where certain quantum particles, such as excitons—bound states of electrons and holes—were thought to maintain exclusive, stable pairings. Traditionally, excitons behave like bosons and are considered monogamous because breaking their electron-hole bonds requires energy. However, experiments led by researchers at the Joint Quantum Institute (JQI) revealed that under extreme electron crowding in a specially engineered layered material, excitons unexpectedly increased their mobility instead of slowing down. This surprising result indicated that excitons could abandon their exclusive partnerships and interact with multiple electrons, effectively breaking the monogamous behavior. The team constructed a material forcing electrons and excitons into a grid of discrete sites, where electrons, as fermions, refused to share sites, initially slowing exciton movement as electron density increased. Yet, once nearly all sites were occupied by electrons, excitons began moving more freely and farther than before, a phenomenon replicated across different samples and experimental setups worldwide