Extreme Many-Body Interactions of Giant Excitons in a Rydberg Blockade

Over the past two decades, Rydberg states have gained prominence as a promising platform for quantum information processing. These states were first recognized in highly excited, hydrogen-like atoms with large principal quantum numbers, n, where it was quickly understood that the giant size of these species instigates significant interactions. In particular, these interactions manifest through long-range dipole-dipole coupling, which gives rise to Rydberg blockade effects, where the presence of one excited state prohibits the nearby excitation of another at the same energy. In this way, the Rydberg blockade naturally leads to the emergence of strongly correlated many-body excitations. Similar phenomena are possible in the solid state, though they are more challenging to access, especially due to the limited number of systems found to host the requisite highly excited states. Specifically, the fundamental excitations of semiconductors, i.e., excitons, serve as the condensed matter analogues of hydrogen-like species and have the potential to lead to intriguing Rydberg blockade effects. In this work, we resolve the ultrafast dynamics of a Rydberg blockade for the first time in the model semiconductor system Cu₂O, for excitons up to n = 7. We discuss the extreme many-body interactions of these giant excitons, with sizes up to ~0.15 μm, as well as the n-dependent recovery bottleneck resulting from extended many-body exciton correlations. Future and ongoing work employing higher-order spectroscopies will also be explored.