Emergence of Unruh prethermalization for uniformly accelerating many-atom system

A uniformly accelerated atom in an inertial vacuum generally thermalizes to a Gibbs state, which is known as the Unruh effect. In contrast, for a noninteracting many-body system coupled to a common massless scalar field, we find that thermalization proceeds in multiple stages: the system first attains a prethermal generalized Gibbs state, before eventual relaxation to the thermal Gibbs state. The prethermal state is protected by emergent conserved quantities; hence, the system behaves like a nearly integrable one, which shows a sharp distinction from the Unruh effect. We coin the term “Unruh prethermalization” to characterize this phenomenon. The measure of entanglement is a good estimation of the lifetime of the prethermal state and is consistent with previous studies. Finally, we show that in such a regime, the dynamics show a Dicke superradiance-type radiation burst before reaching the prethermal state. In contrast, only a monoexponential decay is observed for Unruh thermalization. In addition, to highlight the significance of our results, we compare them with existing experimental observations.