Enhancing light–matter coupling for exploring chaos in the quantum Rabi model

Abstract Accessing chaos in the quantum Rabi model (QRM) usually requires operating far from resonance, combined with ultra- or deep-strong light–matter coupling. This makes direct experiments challenging, so we propose an indirect route based on an anti-squeezing transformation of the bosonic field. This transformation maps a weakly coupled, two-photon driven Jaynes–Cummings model to an effective deep-strong-coupling QRM in the squeezed-light frame. Increasing the squeezing raises both the effective coupling and the atom–field frequency ratio, giving access to the semiclassical QRM regime without intrinsic ultra-strong coupling or large bare detuning. We analyze the chaotic behavior of the effective model using both semiclassical and quantum methods. These complementary diagnostics reveal coexisting regular and chaotic behavior and spectral correlations that depend on energy and squeezing. Long-time quantum features agree qualitatively with the semiclassical classification, whereas short-time criteria are not reliable stand-alone chaos tests in this model. Combining tunable coupling enhancement with these complementary probes provides a practical way to explore QRM chaos. Comparing the probe results also clarifies the limits of each method.