Exploring Nonlinear Dynamics in Waveguide QED Systems

Recent research by Egor S. Vyatkin, Alexander V. Poshakinskiy, and Alexander N. Poddubny explores the nonlinear dynamical Casimir effect and Unruh entanglement within waveguide quantum electrodynamics (QED) systems that feature parametrically modulated coupling. This study, titled "Nonlinear dynamical Casimir effect and Unruh entanglement in waveguide QED with parametrically modulated coupling," was submitted on August 30, 2024, and is available on arXiv under the identifier 2408.17365.

The authors investigate a theoretical model involving an array of two-level qubits that can move relative to a one-dimensional waveguide. This motion can be realized either mechanically or through modulation of the couplings between the qubits and the waveguide. A key finding is that when the frequency of this motion approaches twice the qubit resonance frequency, it leads to the parametric generation of photons and the excitation of the qubits.

The research outlines a comprehensive theoretical framework that combines perturbative diagrammatic techniques with a rigorous master-equation approach to tackle the complexities introduced by quantum nonlinearity and nonequilibrium states. Among the significant effects observed are the directional dynamical Casimir effect, where emitted photon pairs exhibit correlated momenta, and the waveguide-mediated collective Unruh effect, which drives the qubits into a steady state that can exhibit entanglement and phase transitions.

Additionally, the study examines the radiation back-action on qubit motion, which becomes pronounced when subradiant modes in the qubit array are excited. This back-action may significantly alter the mechanical spectra, potentially leading to the emergence of hybrid phonon-biphoton modes. These findings could have implications for advancing quantum technologies and enhancing our understanding of quantum electrodynamics phenomena.