# Frequency-renormalized multipolaron expansion for the quantum Rabi model

## TL;DR

This paper introduces a frequency-renormalized multipolaron expansion method to accurately analyze the ground state of the quantum Rabi model, improving upon previous approaches with variationally optimized parameters.

## Contribution

It extends the polaron and coherent state expansion techniques by incorporating frequency renormalization, enhancing the description of the quantum Rabi model's ground state.

## Key findings

- High efficiency in describing the QRM ground state.
- Potential applicability to more complex light-matter interaction models.
- Improved accuracy over previous methods.

## Abstract

We present a frequency-renormalized multipolaron expansion method to explore the ground state of quantum Rabi model (QRM). The main idea is to take polaron as starting point to expand the ground state of QRM. The polarons are deformed and displaced oscillator states with variationally determined frequency-renormalization and displacement parameters. This method is an extension of the previously proposed polaron concept and the coherent state expansion used in the literature, which shows high efficiency in describing the physics of the QRM. The proposed method is expected to be useful for solving other more complicated light-matter interaction models.