  The ability to generate and control strong long-range interactions via highly
excited electronic states has been the foundation for recent breakthroughs in a
host of areas, from atomic and molecular physics [1, 2] to quantum optics [3,
4] and technology [5-7]. Rydberg excitons provide a promising solid-state
realization of such highly excited states, for which record-breaking orbital
sizes of up to a micrometer have indeed been observed in cuprous oxide
semiconductors [8]. Here, we demonstrate the generation and control of strong
exciton interactions in this material by optically producing two distinct
quantum states of Rydberg excitons. This makes two-color pump-probe experiments
possible that allow for a detailed probing of the interactions. Our experiments
reveal the emergence of strong spatial correlations and an inter-state Rydberg
blockade that extends over remarkably large distances of several micrometers.
The generated many-body states of semiconductor excitons exhibit universal
properties that only depend on the shape of the interaction potential and yield
clear evidence for its vastly extended-range and power-law character.
