# Nonlinear optics in the fractional quantum Hall regime

## TL;DR

This paper demonstrates that polariton-polariton interactions are significantly enhanced in a fractional quantum Hall state, revealing new insights into strongly correlated electronic systems through nonlinear optical measurements.

## Contribution

It shows that fractional quantum Hall states can strongly enhance polariton interactions, opening new avenues for photonic quantum systems and probing quantum Hall states via nonlinear optics.

## Key findings

- Enhanced polariton-polariton interactions in fractional quantum Hall states
- Role of exciton-electron interactions and polaron polaritons in nonlinear response
- Potential for nonlinear optics to reveal fractional quantum Hall properties

## Abstract

Engineering strong interactions between optical photons is a great challenge for quantum science. Envisioned applications range from the realization of photonic gates for quantum information processing to synthesis of photonic quantum materials for investigation of strongly-correlated driven-dissipative systems. Polaritonics, based on the strong coupling of photons to atomic or electronic excitations in an optical resonator, has emerged as a promising approach to implement those tasks. Recent experiments demonstrated the onset of quantum correlations in the exciton-polariton system, showing that strong polariton blockade could be achieved if interactions were an order of magnitude stronger. Here, we report time resolved four-wave mixing experiments on a two-dimensional electron system embedded in an optical cavity, demonstrating that polariton-polariton interactions are strongly enhanced when the electrons are initially in a fractional quantum Hall state. Our experiments indicate that in addition to strong correlations in the electronic ground state, exciton-electron interactions leading to the formation of polaron polaritons play a key role in enhancing the nonlinear optical response. Besides potential applications in realization of strongly interacting photonic systems, our findings suggest that nonlinear optical measurements could provide information about fractional quantum Hall states that is not accessible in linear optical response.