paper

Light-matter excitations in the ultra-strong coupling regime

arXiv:0808.3720 · doi:10.1103/PhysRevB.79.201303

Abstract

In a microcavity, light-matter coupling is quantified by the vacuum Rabi frequency . When 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 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.

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