Observation of Ergodicity Breaking and Quantum Many-Body Scars in Spinor Gases

We experimentally and theoretically demonstrate that spinor gases driven by spin-flopping fields are excellent platforms for investigating ergodicity breaking and quantum scarring. We observe that specific initial states remain nonthermal at weak driving despite the majority of states thermalizing, which constitutes clear evidence of quantum many-body scars (QMBSs). As the driving strength increases, the experimental system undergoes a smooth transition from integrable to weakly ergodicity breaking, which supports QMBSs, and then to fully thermal. This is in agreement with the theoretical spectra, which predict towers of states dissolving with increasing driving strength. This Letter advances the study of QMBSs and quantum scars with applications to, e.g., quantum information storage.