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

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 Schrödinger cat state.

9 pages + 3 page appendix, 8 figures

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• Enhancing cavity QED via anti-squeezing: synthetic ultra-strong coupling
• Generalized adiabatic approximation to the quantum Rabi model
• Non-orthogonal qubit states expansion for the asymmetric quantum Rabi model
• Nonclassicality of open circuit QED systems in the deep-strong coupling regime
• Fast transport and splitting of spin-orbit-coupled spin-1 Bose-Einstein Condensates
• Tripartite quantum Rabi model with trapped Rydberg ions