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arXiv2026

Dissipation-induced Sachdev-Ye-Kitaev physics in many-body cavity quantum electrodynamics

We show that cavity quantum electrodynamics (QED) devices can realize dissipative Sachdev-Ye-Kitaev (SYK) physics, a paradigmatic setting for quantum chaos in open many-body systems. Ultracold fermions with disordered, all-to-all cavity-mediated interactions provide two complementary routes: atomic spontaneous emission in a single-mode cavity and photon leakage from a multimode cavity. Strikingly, both converge to the same non-Hermitian random-matrix universality despite originating from integrable and chaotic closed-system limits, respectively. In the single-mode case, dissipation therefore creates quantum chaos from an integrable Hamiltonian. We trace this convergence to a tunable growth in dissipative rank, controlled, respectively, by the Lamb-Dicke parameter and the cavity-mode spacing. The resulting chaos leaves a dynamical fingerprint: a crossover from long-lived prethermal memory to rapid thermalization, visible in single-atom-resolved densities.

quant-ph↗

arXiv2025

Coupling between ferroelectric distortions and excitonic properties in PbTiO$_3$

PbTiO$_3$ is a ferroelectric perovskite semiconductor with favourable electronic and optical properties, making it suitable for a wide range of applications, including photo-catalysis and (opto)electronic devices. Despite its relevance, an accurate ab-initio description of the optical absorption spectrum and of the impact of ferroelectric distortion on the excitonic properties is still lacking. We combine $G_0W_0$ and Bethe-Salpeter Equation calculations to investigate the electronic and optical properties of PbTiO$_3$, tracking the evolution of its excitonic spectrum along the transition from the cubic paraelectric to the tetragonal ferroelectric phase. As the polar distortion increases, the first absorption peak of the cubic phase splits into two distinct features due to symmetry breaking, which partially lifts the degeneracy of the underlying excitonic state. Crucially, the distortion further introduces an in-plane/out-of-plane anisotropy in the spectra and controls the energy separation between the resulting excitonic branches. These findings highlight the potential for tuning the optical absorption properties of PbTiO$_3$ via the application of an external electric field.

cond-mat.mtrl-sci↗