Strongly nonlinear nanocavity exciton-polaritons in gate-tunable monolayer semiconductors

TL;DR

This paper demonstrates highly nonlinear, gate-tunable exciton-polaritons in a monolayer semiconductor coupled to a nanocavity, enabling ultralow-energy all-optical switching with potential for quantum information applications.

Contribution

It experimentally realizes strongly nonlinear exciton-polaritons in a monolayer semiconductor nanocavity system, revealing new mechanisms for nonlinearity at ultralow energies.

Findings

Achieved all-optical switching at ~4 fJ energy levels.

Observed exciton dephasing leading to breakdown of strong coupling.

Demonstrated gate-tunable control of polariton nonlinearity.

Abstract

Strong coupling between light and matter in an optical cavity provides a pathway to giant polariton nonlinearity, where effective polariton-polariton interactions are mediated by materials' nonlinear responses. The pursuit of such enhanced nonlinearity at low optical excitations, potentially down to the single-particle level, has been a central focus in the field, inspiring the exploration of novel solid-state light-matter systems. Here, we experimentally realize extremely nonlinear and robust cavity exciton-polaritons by coupling a charge-tunable MoSe2 monolayer to a photonic crystal nanocavity. We show that the observed polariton nonlinearity arises from increased exciton dephasing at high populations, leading to diminished exciton-photon coupling and ultimately the breakdown of the strong coupling condition. Remarkably, the strong mode confinement of the nanocavity enables all-optical switching of the cavity spectrum at ultralow optical excitation energies, down to ~4 fJ, on picosecond timescales. Our work paves the way for further exploration of 2D nonlinear exciton-polaritons, with promising applications in both classical and quantum all-optical information processing.