Tailored subcycle nonlinearities of ultrastrong light-matter coupling

TL;DR

This paper investigates the nonlinear behavior of hybrid light-matter states in an ultrastrong coupling regime where both the Rabi frequency and vacuum Rabi frequency are comparable to the light's carrier frequency, revealing novel subcycle nonlinearities.

Contribution

It introduces a new regime of ultrastrong coupling where tailored subcycle nonlinearities occur, violating normal-mode approximation while maintaining ultrastrong coupling.

Findings

Subcycle pump-probe and multi-wave mixing nonlinearities observed.

Normal-mode approximation is violated in the ultrastrong regime.

Potential applications in non-classical light sources and quantum technologies.

Abstract

We explore the nonlinear response of tailor-cut light-matter hybrid states in a novel regime, where both the Rabi frequency induced by a coherent driving field and the vacuum Rabi frequency set by a cavity field are comparable to the carrier frequency of light. In this previously unexplored strong-field limit of ultrastrong coupling, subcycle pump-probe and multi-wave mixing nonlinearities between different polariton states violate the normal-mode approximation while ultrastrong coupling remains intact, as confirmed by our mean-field model. We expect such custom-cut nonlinearities of hybridized elementary excitations to facilitate non-classical light sources, quantum phase transitions, or cavity chemistry with virtual photons.