Quantum Optical Properties of Highly-Excited Semiconductors

Dr. Valentin Walther, Assistant Professor
James Tarpo Jr. and Margaret Tarpo Department of Chemistry, Department of Physics and Astronomy
Purdue University
West Lafayette, Indiana, 47907

Controlling individual photons and inducing them to interact lies at the heart of future quantum technologies. From secure communication to scalable quantum computing, the ability to engineer strong photon-photon interactions is a key requirement. Yet in conventional optical materials, photons barely interact at all. This project explores an emerging solution: using Rydberg excitons—highly excited bound states of electrons and holes in semiconductors—to mediate strong optical nonlinearities and unlock new modes of quantum light control.

Rydberg excitons combine two powerful features: they exhibit the strong inter-particle forces typical of atomic Rydberg states, while being embedded in solid-state systems that are more easily integrated into scalable devices. Realizing this potential, however, remains a major challenge. These excitons exist within complex semiconductor environments that modify their behavior in ways we do not yet fully understand. To make use of Rydberg excitons as a quantum platform, we need new theoretical tools that capture how they interact with each other, and with photons, to give rise to emergent quantum optical phenomena from the few- to many-body regimes.

This project aims to build that theoretical foundation, enabling predictive models of Rydberg excitons and their role in generating and manipulating quantum states of light. The research will focus on two semiconductor systems with leading potential: cuprous oxide (Cu2O), which hosts well-defined Rydberg excitons with long lifetimes, and transition metal dichalcogenide (TMD) monolayers, whose atomically thin geometry offers enhanced optical access. In Cu2O, the work will explore how microwave fields, phonons, and cavity design influence many-body exciton dynamics and enable strong photon blockade effects. In TMDs, the project will investigate how geometry, interfaces, and polarization affect exciton interactions and surface wave propagation, with the goal of realizing robust, material-based sources of quantum light.

These studies will lay the groundwork for next-generation quantum optical technologies based on scalable and integrable materials. The project builds on prior advances in nonlinear optics, quantum theory, and exciton physics, and will proceed in close collaboration with experimental groups to ensure that theoretical predictions are grounded in practical feasibility and have real-world impact.

This research was selected for funding by the Office of Basic Energy Sciences.
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