Comment on `Parameter-dependent unitary transformation approach for quantum Rabi model'

TL;DR

This paper critically examines and refutes a recent claimed exact solution to the quantum Rabi model, identifying it as an approximation rather than an exact solution due to fundamental errors.

Contribution

It provides a detailed critique of the previous solution, clarifying the correct approach and highlighting the importance of proper term inclusion in the quantum Rabi model.

Findings

The previous solution is an approximation, not an exact solution.

Neglecting certain terms leads to a simplified model akin to Jaynes-Cummings.

The correct solution requires careful treatment of all Hamiltonian terms.

Abstract

We discuss the elementary errors in D.G. Zhang's [New. J. Phys. 23, 093014 (2021)] claimed exact solution of the quantum Rabi model. The erroneous solution is seen to be nothing more than the combined solution of the simpler Jaynes-Cummings and anti-Jaynes-Cummings models obtained by neglecting terms in the model Hamiltonian.