Equivalence between non-commutative harmonic oscillators and two-photon quantum Rabi models
Ryosuke Nakahama
TL;DR
The paper shows that the eigenproblem of $H_{NCHO}^{(\alpha,\beta,\eta)}$ is equivalent to an eigenproblem for $\widetilde{H}_{2QRM}^{(g,\Delta,\varepsilon)}$ up to the unitary factor $e^{\frac{\pi i}{4}H}$ and a similarity transform, and that on the even/odd subspaces this reduces to a holomorphic-disk differential equation. It builds explicit parameter correspondences and uses a sequence of unitary maps to translate the problem into disk-model terms. A confluence limit $\nu \to \infty$ yields a degeneration to the one-photon QRM, clarifying covering relations between the two- and one-photon models. The work thus provides a rigorous link between a mathematical non-commutative oscillator and quantum Rabi models, with potential number-theoretic insights and a framework for further spectral analysis.
Abstract
We prove that the non-commutative harmonic oscillator on $L^2(\mathbb{R})\otimes\mathbb{C}^2$ introduced by Parmeggiani and Wakayama is equivalent to the two-photon quantum Rabi model, and they are also equivalent to a holomorphic differential equation on the unit disk. The confluence process of this differential equation and the relation with the one-photon quantum Rabi model are also discussed.
