A two-interacting-qubit quantum Rabi-like model with vanishing transverse fields on the qubit-pair is studied. Independently of the coupling regime, this model can be exactly and unitarily reduced to two independent single-spin quantum Rabi models, where the spin-spin coupling plays the role of the transverse field. This transformation and the analytical treatment of the single-spin quantum Rabi model provide the key to prove the integrability of our model. The existence of different first-order quantum phase transitions, characterized by discontinuous two-spin magnetization, mean photon number and concurrence, is brought to light.
@article{arxiv.2211.07207,
title = {Quantum phase transitions for an integrable quantum Rabi-like model with two interacting qubits},
author = {Roberto Grimaudo and Antonio S. M. de Castro and Antonino Messina and Enrique Solano and Davide Valenti},
journal= {arXiv preprint arXiv:2211.07207},
year = {2023}
}