arXiv subjects

Si-Han Shang

Publications and source records attributed to Si-Han Shang.

6 recordsLinked to original sources

arXiv2026

Topology-dependent relativistic degradation of multipartite entanglement

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.

quant-ph↗

arXiv2026

Non-monotonic evolution of multipartite entanglement under the Unruh effect

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.

gr-qc↗

arXiv2025

Does the survival and sudden death of quadripartite steering in curved spacetime truly depend on multi-directionality?

We systematically investigate the directional dependence of Gaussian quadripartite quantum steering and its redistribution among different modes in the background of a Schwarzschild black hole. For physically accessible sectors, we identify three distinct behaviors: (i) steering from non-gravitational to gravitational observers undergoes sudden death at maximal asymmetry with the Hawking temperature, marking the crossover from two-way to one-way steerability; (ii) steering in the opposite direction decays monotonically and vanishes only in the extreme black hole limit, highlighting its directional sensitivity to spacetime curvature; (iii) steering from hybrid gravitational-non-gravitational partitions to non-gravitational mode persists at a finite asymptotic value set by the initial squeezing parameter. Moreover, all inaccessible steerings generated by the Hawking effect exhibit an intrinsic asymmetry, with their specific behavior being strongly dependent on the steering direction.

gr-qc↗

arXiv2025

Influence of dark matter on quantum entanglement and coherence in curved spacetime

Dark matter (DM) remains undetected, and developing theoretical models such as the promising perfect fluid dark matter (PFDM) is a key challenge in modern cosmology. In this work, we investigate the quantum characteristics of PFDM by analyzing the behavior of quantum entanglement and coherence for both fermionic and bosonic fields near a Schwarzschild black hole embedded in a PFDM halo. Our results reveal that PFDM can either enhance or degrade quantum entanglement and coherence, depending sensitively on its density. Notably, bosonic entanglement shows greater susceptibility to PFDM effects compared to fermionic entanglement, while fermionic coherence exhibits a stronger dependence on PFDM than its bosonic counterpart. These findings highlight the necessity of selecting appropriate quantum probes for DM detection based on the type of quantum resources, as different quantum fields exhibit significantly different responses to PFDM in curved spacetime.

gr-qc↗

arXiv2025

Does acceleration always degrade quantum entanglement for tetrapartite Unruh-DeWitt detectors?

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.

gr-qc↗

arXiv2024

Quantum steering for different types of Bell-like states in gravitational background

In a relativistic framework, it is generally accepted that quantum steering of maximally entangled states provide greater advantages in practical applications compared to non-maximally entangled states. In this paper, we investigate quantum steering for four different types of Bell-like states of fermionic modes near the event horizon of a Schwarzschild black hole. In some parameter spaces, the peak of steering asymmetry corresponds to a transition from two-way to one-way steerability for Bell-like states under the influence of the Hawking effect. It is intriguing to find that the fermionic steerability of the maximally entangled states experiences sudden death with the Hawking temperature, while the fermionic steerability of the non-maximally entangled states maintains indefinite persistence at infinite Hawking temperature. In contrast to prior research, this finding suggests that quantum steering of non-maximally entangled states is more advantageous than that of maximally entangled states for processing quantum tasks in the gravitational background. This surprising result overturns the traditional idea of ``the advantage of maximally entangled steering in the relativistic framework" and provides a new perspective for understanding the Hawking effect of the black hole.

gr-qc↗