Rydberg Excitons—A Novel Platform for On-Chip Rydberg-Based Quantum Technologies

Strong photon-photon interaction is the holy grail of quantum optics, as it is essential for the development of photonic quantum networks and information processors which could revolutionize modern information technologies. However, photons in a vacuum do not interact with each other, so a nonlinear material is needed to mediate such interactions. Excitons, semiconductor electron-hole pairs, are promising candidates for creating such nonlinearities. Similar to their atomic counterparts, excitons can be promoted to highly excited Rydberg states with high principal quantum numbers. These states have exaggerated wavefunctions and interact strongly with each other via long-range strong dipole-dipole and Van der Waals potentials. These potentials perturb the energy level structure of nearby atoms such that they can no longer be excited to the same Rydberg state. This effect, known as Rydberg blockade, facilitates the deterministic single-photon nonlinearities required in quantum computing. Rydberg excitons in solid-state platforms incorporate the exceptional nonlinearities of Rydberg states on a scalable, solid-state host. As such, a suitable material system for Rydberg excitons is indispensable for harnessing the unique properties of excitons in scalable, on-chip quantum devices.<br/><br/>So far, cuprous oxide (Cu₂O) is the only known semiconductor where Rydberg excitons with principal quantum numbers up to n = 25 have been observed. It has a high binding energy and symmetric lattice structure, which allow it to host many Rydberg exciton states without undergoing thermal ionization. However, natural bulk cuprous oxide cannot be made defect-free, so a more controlled fabrication process is required to grow high-purity, customizable, synthetic, cuprous oxide. Thin-film cuprous oxide samples with thicknesses below the blockade radius are of particular interest because they more easily facilitate the observation and utilization of Rydberg blockade effect.<br/><br/>In this talk, we will present spectroscopic absorption and photoluminescence measurements of Rydberg excitons from a synthetic thin-film of cuprous oxide deposited on a transparent substrate. Our studies demonstrate Rydberg exciton states up to n=7, and their power and temperature-dependent behavior. We will also report the formation of cavity Rydberg polaritons and lifetime enhancement of exciton states via strong coupling with cavity photons. Finally, we will report on the behavior of Rydberg excitons in a sample of Cu₂O coated with the 2D material ruthenium chloride (RuCl₃) and how they behave near its magnetic phase transition temperature. Our results will pave the way for CMOS compatible, on-chip, Rydberg based quantum systems with a wide range of applications in solid-state quantum information processing, non-classical light sources, quantum simulators, quantum metrology, and quantum sensing.