# Doubly dressed bosons - exciton-polaritons in a strong terahertz field

## TL;DR

This paper reports the discovery of a new quasiparticle, a doubly dressed exciton-polariton, formed by coupling a semiconductor exciton with both near-infrared and terahertz photons, especially in the ultra-strong terahertz coupling regime.

## Contribution

It introduces the concept of a doubly dressed exciton-polariton, combining matter and two light fields, with a comprehensive quantum mechanical analysis confirming their unique properties.

## Key findings

- Existence of a novel exciton quasiparticle doubly dressed with infrared and terahertz photons
- The quasiparticle exhibits strong dependence on terahertz field intensity
- Theoretical analysis confirms the bosonic nature and complex internal structure

## Abstract

We demonstrate the existence of a novel quasiparticle: an exciton in a semiconductor doubly dressed with two photons of different wavelengths: near infrared cavity photon and terahertz (THz) photon, with the THz coupling strength approaching the ultra-strong coupling regime. This quasiparticle is composed of three different bosons, being a mixture of a matter-light quasiparticle. Our observations are confirmed by a detailed theoretical analysis, treating quantum mechanically all three bosonic fields. The doubly dressed quasiparticles retain the bosonic nature of their constituents, but their internal quantum structure strongly depends on the intensity of the applied terahertz field.