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arXiv:2509.05816 · Physical review. D/Physical review. D.

Emergence of Unruh prethermalization for uniformly accelerating many-atom system

Saptarshi Saha, Chiranjeeb Singha, Pragna Das, Arpan Chatterjee

Published Feb 27, 2026• 1 citation
arXivHTMLPDF

Abstract

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.

DOI
10.1103/nq1q-3md9

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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.
The entanglement generated for a uniformly accelerated two-atom system in vacuum during its evolution may increase with acceleration, while that for a static one in a thermal bath always decreases monotonically with temperature. This phenomenon is named as the anti-Unruh effect in terms of the entanglement generated. In this paper, we study the effects of the interatomic interaction induced by the electromagnetic vacuum fluctuations on the entanglement dynamics of two uniformly accelerated atoms. We show that the anti-Unruh phenomenon may exist or disappear depending critically on the configuration of the orientation of the atomic polarization and the directions of the uniform acceleration and the interatomic separation. This is in sharp contrast to the scalar-field case, in which the anti-Unruh phenomenon is always lost when the environment-induced interatomic interaction is considered.
We study, in the framework of open systems, the entanglement generation of two independent uniformly accelerated atoms in interaction with the vacuum fluctuations of massless scalar fields subjected to a reflecting plane boundary. We demonstrate that, with the presence of the boundary, the accelerated atoms exhibit distinct features from static ones in a thermal bath at the corresponding Unruh temperature in terms of the entanglement creation at the neighborhood of the initial time. In this sense, accelerated atoms in vacuum do not necessarily have to behave as if they were static in a thermal bath at the Unruh temperature.
We investigate the transition rates of uniformly accelerated two-level single and entangled atomic systems in empty space as well as inside a cavity. We take into account the interaction between the systems and a massless scalar field from the viewpoint of an instantaneously inertial observer and a coaccelerated observer, respectively. The upward transition occurs only due to the acceleration of the atom. For the two-atom system, we consider that the system is initially prepared in a generic pure entangled state. In the presence of a cavity, we observe that for both the single and the two-atom cases, the upward and downward transitions are occurred due to the acceleration of the atomic systems. The transition rate manifests subtle features depending upon the cavity and system parameters, as well as the initial entanglement. It is shown that no transition occurs for a maximally entangled superradiant initial state, signifying that such entanglement in the accelerated two-atom system can be preserved for quantum information processing applications. Our analysis comprehensively validates the equivalence between the effect of uniform acceleration for an inertial observer and the effect of a thermal bath for a coaccelerated observer, in free space as well as inside a cavity, if the temperature of the thermal bath is equal to the Unruh temperature.
Abstract We study the radiative process of two entangled two-level atoms uniformly accelerated in a thermal bath, coupled to a massless scalar field. First, by using the positive frequency Wightman function from the Minkowski modes with a Rindler transformation we provide the transition probabilities for the transitions from maximally entangled symmetric and anti-symmetric Bell states to the collective excited or ground state in (1 + 1) and (1 + 3) dimensions. We observe a possible case of anti-Unruh-like event in these transition probabilities, though the (1+1) and (1+3) dimensional results are not completely equivalent. We infer that thermal bath plays a major role in the occurrence of the anti-Unruh-like effect, as it is also present in the transition probabilities corresponding to a single detector in this case. Second, we have considered the Green’s functions in terms of the Rindler modes with the vacuum of Unruh modes for estimating the same. Here the anti-Unruh effect appears only for the transition from the anti-symmetric state to the collective excited or ground state. It is noticed that here the (1 + 1) and (1 + 3) dimensional results are equivalent, and for a single detector, we do not observe any anti-Unruh effect. This suggests that the entanglement between the states of the atoms is the main cause for the observed anti-Unruh effect in this case. In going through the investigation, we find that the transition probability for a single detector case is symmetric under the interchange between the thermal bath’s temperature and the Unruh temperature for Rindler mode analysis; whereas this is not the case for Minkowski mode. We further comment on whether this observation may shed light on the analogy between an accelerated observer and a real thermal bath. An elaborate investigation for the classifications of our observed anti-Unruh effects, i.e., either weak or strong anti-Unruh effect, is also thoroughly demonstrated.
This paper explores the phenomenon of universal prethermalization in out-of-equilibrium interacting Bose-Fermi degenerate systems. Prethermalization, a transient non-equilibrium state characterized by a quasi-stationary distribution that is thermal with respect to a restricted set of effective conserved quantities, has emerged as a fundamental concept in the understanding of isolated quantum many-body systems far from equilibrium. We specifically focus on the unique interplay between bosonic and fermionic degrees of freedom, which introduces novel pathways for relaxation and distinct characteristics of prethermal plateaus. The universality of prethermal dynamics, implying independence from microscopic details and initial conditions within certain regimes, is investigated in the context of interspecies interactions, density imbalances, and dimensionality. We review the theoretical frameworks, including mean-field descriptions, effective Hamiltonians, and kinetic equations, alongside experimental observations in ultracold atomic gases that provide a fertile ground for studying such non-equilibrium phenomena. The emergence of universal scaling laws and the role of conservation laws in defining the prethermal state are discussed, paving the way for a deeper understanding of thermalization processes and the persistence of non-equilibrium states in complex quantum matter.
Abstract We study, in the framework of open quantum systems, the entanglement dynamics for a quantum system composed of two uniformly accelerated Unruh-Dewitt detectors interacting with a bath of massive scalar fields in the Minkowski vacuum. We find that the entanglement evolution for the quantum system coupled with massive fields is always slower compared with that of the one coupled with massless fields, and this time-delay effect brought about by the field being massive can however be counteracted by a large enough acceleration, in contrast to the case of a static quantum system in a thermal bath, where this time delay is not affected by the temperature. Remarkably, the maximal concurrence of the quantum system generated during evolution may increase with acceleration for any inter-detector separation while that for static ones in a thermal bath decreases monotonically with temperature, and this can be considered as an anti-Unruh effect in terms of the entanglement generated.