Emergent SSH physics and localization in a cavity--atom system beyond the rotating-wave approximation

Abstract

We investigate a cavity--atom system beyond the rotating-wave approximation and recast its dynamics as an effective tight-binding problem in the excitation-number basis. The same experimentally relevant light--matter platform exhibits two distinct regimes controlled by the photon number. In the large-photon-number regime, the hopping amplitudes become nearly uniform and the effective lattice reduces to a dimerized SSH-type chain subject to a linear energy gradient. The spectrum then organizes into one or two Wannier--Stark ladders, giving rise to controllable Bloch and Bloch--Zener oscillations and quantitatively explaining the observed revival patterns. In the small-photon-number regime, the intrinsic $\sqrt{\bar n+(\cdots)}$ dependence produces a pronounced hopping deformation, namely dimerized couplings that increase along the excitation-number lattice. This deformation reshapes the density of states, enhances collective localization, and generates an energy-resolved spatial bias of the eigenstates. The corresponding real-time dynamics displays direction-dependent anomalous diffusion together with Bloch-like revivals and beat phenomena in selected parameter windows. Our results show that the same cavity--atom platform can realize both emergent ladder spectra and hopping-induced localization in excitation-number space.