Ground-state phase diagram of the quantum Rabi model

TL;DR

This paper maps the ground-state phase diagram of the quantum Rabi model, revealing new polaronic states and scaling behaviors across different coupling regimes, with implications for understanding light-matter interactions.

Contribution

It provides the first detailed ground-state phase diagram of the full quantum Rabi model, identifying novel polaronic states and hidden scaling behaviors.

Findings

Discovery of quadpolaron and bipolaron states in the QRM

Revelation of an overweighted antipolaron in the quadpolaron state

Identification of a hidden scaling behavior related to symmetry breaking

Abstract

The Rabi model plays a fundamental role in understanding light-matter interaction. It reduces to the Jaynes-Cummings model via the rotating-wave approximation, which is applicable only to the cases of near resonance and weak coupling. However, recent experimental breakthroughs in upgrading light-matter coupling order require understanding the physics of the full quantum Rabi model (QRM). Despite the fact that its integrability and energy spectra have been exactly obtained, the challenge to formulate an exact wavefunction in a general case still hinders physical exploration of the QRM. Here we unveil a ground-state phase diagram of the QRM, consisting of a quadpolaron and a bipolaron as well as their changeover in the weak-, strong- and intermediate-coupling regimes, respectively. An unexpected overweighted antipolaron is revealed in the quadpolaron state, and a hidden scaling behavior relevant to symmetry breaking is found in the bipolaron state. An experimentally accessible parameter is proposed to test these states, which might provide novel insights into the nature of the light-matter interaction for all regimes of the coupling strengths.