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arXiv:2601.02976 · Journal of High Energy Physics

Does relativistic motion really freeze initially maximal entanglement?

Si-Han Li, Hui-Chen Yang, Rui-Yang Xu, Shu-Min Wu

gr-qcquant-phSubmitted Jan 6, 2026• Announced Jan 7, 2026• 3 citations
v1 · Jan 6, 2026v2 · Mar 30, 2026
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Abstract

We investigate the relativistic dynamics of quantum entanglement in a four-qubit cluster ($CL_4$) state using a fully operational Unruh-DeWitt detector framework. Contrary to the widely held expectation that the Unruh effect inevitably degrades initially maximal entanglement, we demonstrate that the 1-3 bipartite entanglement of the $CL_4$ state remains strictly maximal for all accelerations, including the infinite-acceleration limit. This result uncovers a previously unexplored phenomenon, namely the ``complete freezing of initially maximal entanglement" under relativistic motion. To the best of our knowledge, this is the first identification and systematic characterization of such a phenomenon within a relativistic framework. These findings overturn the conventional view that acceleration universally diminishes maximal entanglement and establish the $CL_4$ state as a promising resource for quantum information processing in non-inertial or curved-spacetime settings.

Journal reference
JHEP 03 (2026) 218
DOI
10.1007/JHEP03(2026)218
Comments
19 pages, 4 figures

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We investigate the relativistic dynamics of quantum entanglement in a four-qubit cluster (CL4CL_4CL4​) state using a fully operational Unruh-DeWitt detector framework. Contrary to the widely held expectation that the Unruh effect inevitably degrades initially maximal entanglement, we demonstrate that the 1-3 bipartite entanglement of the CL4CL_4CL4​ state remains strictly maximal for all accelerations, including the infinite-acceleration limit. This result uncovers a previously unexplored phenomenon, namely the ``complete freezing of initially maximal entanglement" under relativistic motion. To the best of our knowledge, this is the first identification and systematic characterization of such a phenomenon within a relativistic framework. These findings overturn the conventional view that acceleration universally diminishes maximal entanglement and establish the CL4CL_4CL4​ state as a promising resource for quantum information processing in non-inertial or curved-spacetime settings.
Gravitational effects associated with black holes are widely believed to universally degrade quantum entanglement, with the loss of maximal entanglement being particularly severe and even irreversible for bosonic fields. In this work, we investigate the entanglement properties of the four-qubit cluster state (CL4CL_4CL4​) for fermionic fields in the curved spacetime of a Schwarzschild black hole. Remarkably, we uncover a counterintuitive phenomenon: as the Hawking temperature increases, quantum entanglement (111-333 tangle) of the CL4CL_4CL4​ state remains strictly constant, indicating a ``complete freezing of initially maximal entanglement". This constitutes the first explicit example in which maximal entanglement remains perfectly preserved in a black hole environment, defying the conventional expectation that gravitational effects can only suppress maximal quantum correlations. Moreover, our results indicate that, within a relativistic framework, the CL4CL_4CL4​ state constitutes a high-quality quantum resource with potential applications in relativistic quantum information processing, and may significantly improve the performance of such protocols.
This thesis considers entanglement, an important resource for quantum information processing tasks, while taking into account the theory of relativity. Not only is this a more complete description of quantum information, but it is necessary to fully understand quantum information processing tasks done by systems in arbitrary motion. \n \nIt is shown that accelerated measurements on the vacuum of a free Dirac spinor field results in an entangled state for an inertial observer. The physical mechanism at work is the Davies-Unruh effect. The entanglement produced increases as a function of the acceleration, reaching maximal entanglement in the asymptotic limit of infinite acceleration. \n \nThe dynamics of entanglement between two Unruh-DeWitt detectors, one stationary and the other undergoing non-uniform acceleration, was studied numerically. In the ultraweak coupling limit, the entanglement decreases as a function of time for the parameters considered and decreases faster than if the moving detector had had a uniform acceleration.
We investigate the behavior of tetrapartite entanglement in a four-qubit Dicke state under relativistic motion by employing the Unruh-DeWitt detector model, where one detector undergoes uniform acceleration. We show that the entanglement exhibits a non-monotonic evolution: it first decreases and subsequently increases toward a finite value as the acceleration grows. In contrast to the conventional view that the Unruh effect leads to a monotonic degradation of multipartite entanglement, our results demonstrate that it can instead enhance multipartite entanglement within a finite parameter regime. This behavior reveals a dual role of the Unruh effect in multipartite systems. Our findings therefore provide a refined understanding of relativistic multipartite quantum correlations, indicating that Dicke states constitute more robust multipartite quantum resources against Unruh-induced decoherence and may offer advantages for relativistic quantum information processing tasks.
The influence of relativistic motion on quantum entanglement is commonly attributed to acceleration-induced thermal noise. Here we show that, for asymmetric multipartite states, the topology of entanglement can become equally important. Considering a three-qubit Star state in the Unruh-DeWitt detector framework, we compare two inequivalent acceleration configurations in which either the central or a peripheral qubit undergoes uniform acceleration. We demonstrate that these physically equivalent accelerations lead to qualitatively different entanglement dynamics: acceleration of a peripheral qubit induces a revival of one-tangle that is absent when the central qubit accelerates, whereas genuine tripartite entanglement decays monotonically but with markedly different robustness. Our results uncover a topology-dependent mechanism for relativistic entanglement degradation, showing that the response of multipartite quantum correlations is determined jointly by Unruh thermalization and the structural role of the accelerated subsystem. This work identifies asymmetric quantum networks as a distinct platform for controlling relativistic quantum resources.
A bstract Previous studies have shown that the Unruh effect completely destroys quantum entanglement and coherence of bipartite states, as modeled by entangled Unruh-DeWitt detectors. But does the Unruh effect have a different impact on quantum entanglement of multipartite states within this framework? In this paper, we investigate the influence of the Unruh effect on 1 − 3 entanglement in the context of entangled tetrapartite Unruh-DeWitt detectors. We find that quantum entanglement of tetrapartite W state first decreases to a minimum value and then increases to a fixed value with the growth of the acceleration. This indicates that the Unruh effect can, under certain conditions, enhance quantum entanglement. In other words, the Unruh effect plays a dual role in the behavior of quantum entanglement-both diminishing and enhancing it. This discovery challenges and overturns the traditional view that the Unruh effect is solely detrimental to quantum entanglement and coherence in entangled Unruh-DeWitt detectors, offering a fresh and profound perspective on its impact.
While the Unruh effect has traditionally been studied under the assumption of uniform acceleration, a simplification motivated by experimental considerations, it is not necessarily true for all non-inertial motions. We propose a novel approach for the indirect detection of the Unruh effect without relying on the former restriction. Previous studies have shown that probing the decoherence of an Unruh-DeWitt detector can significantly reduce the acceleration required for observing the effect by several orders of magnitude compared to earlier proposals. Building on this idea, we develop a theoretical framework describing a non-inertial observer equipped with a detector undergoing non-uniform, time-dependent acceleration. We show that, in a non-uniformly accelerated Rindler spacetime, the particle distribution perceived in the Minkowski vacuum acquires a time-dependent modification of the standard Unruh spectrum. Furthermore, we demonstrate that the inclusion of quantum entanglement leads to a deformation of the Minkowski vacuum into squeezed states.