# Simple variational ground state and pure cat state generation in the quantum Rabi model

## TL;DR

This paper presents a simple variational approach to approximate the ground state of the quantum Rabi model, revealing a regime where the ground state is a nearly pure Schrödinger cat state, with high fidelity across all parameters.

## Contribution

A new, physically-motivated variational ground state for the quantum Rabi model using Gaussian cavity and nonorthogonal qubit states, effective in all coupling regimes.

## Key findings

- High-fidelity approximation of the ground state across all regimes
- Identification of a regime with nearly pure Schrödinger cat ground state
- Development of a heuristic understanding of ground state evolution

## Abstract

We introduce a simple, physically-motivated variational ground state for the quantum Rabi model, and demonstrate that it provides a high-fidelity approximation of the true ground state in all parameter regimes (including intermediate and strong coupling regimes). Our variational state is constructed using Gaussian cavity states and nonorthogonal qubit pointer states, and contains only three variational parameters. We use our state to develop a heuristic understanding of how the ground state evolves with increasing coupling, and find a previously unexplored regime where the ground state corresponds to the cavity being in a nearly pure Schr\"odinger cat state.