Light-matter excitations in the ultra-strong coupling regime

TL;DR

This paper demonstrates the experimental observation of ultra-strong light-matter coupling in a quantum-well microcavity, revealing anti-resonant effects and photon-energy renormalization at room temperature.

Contribution

First experimental evidence of ultra-strong coupling regime in a quantum-well microcavity through direct dispersion measurements.

Findings

Observation of anti-resonant light-matter coupling

Photon-energy renormalization of the vacuum field

Signatures of ultra-strong coupling at room temperature

Abstract

In a microcavity, light-matter coupling is quantified by the vacuum Rabi frequency $\Omega_R$. When $\Omega_R$ is larger than radiative and non-radiative loss rates, the system eigenstates (polaritons) are linear superposition of photonic and electronic excitations, a condition actively investigated in diverse physical implementations. Recently, a quantum electrodynamic regime (ultra-strong coupling) was predicted when $\Omega_R$ becomes comparable to the transition frequency. Here we report unambiguous signatures of this regime in a quantum-well intersubband microcavity. Measuring the cavity-polariton dispersion in a room-temperature linear optical experiment, we directly observe the anti-resonant light-matter coupling and the photon-energy renormalization of the vacuum field.