arXiv subjects

Samira Elghaayda

Publications and source records attributed to Samira Elghaayda.

9 recordsLinked to original sources

arXiv2025

Basis-independent coherence and its distribution in de Sitter spacetime

Quantum coherence in curved spacetime offers a fresh window into the interplay between gravity, thermality, and quantum resources. While previous work has shown that Markovian evolution can generate entanglement and other nonclassical correlations in de Sitter backgrounds, the basis-dependent nature of coherence has so far limited its unambiguous interpretation. Here, we introduce a basis-independent framework to quantify not only the total coherence of two comoving detectors, but also its collective and localized contributions, and we trace how each of these decomposed measures varies with the inverse of Gibbons-Hawking temperature. By treating the detectors as open quantum systems interacting with a massless scalar field in the Bunch-Davies and squeezed alpha-vacua, we find that non-thermal squeezing substantially enhances extractable coherence, even under strong thermal effects. Our results demonstrate how basis-independent coherence in de Sitter spacetime can serve as a robust resource for relativistic quantum information protocols.

gr-qc↗

arXiv2025

Dimeric perylene-bisimide organic molecules: Application as a quantum battery

This work introduces a unified theoretical framework for quantum batteries (QBs) constructed from thermally equilibrated arrays of dimeric perylene bisimide (PBI) molecules. These organic dimers, with chemically tunable transition energies and dipole-dipole interactions, constitute a scalable and practical platform for quantum energy storage. Using exact diagonalization of the Gibbs state supported by analytic and numerical resource-theoretic tools, we evaluate four performance metrics: ergotropy, instantaneous charging power, storage capacity, and quantum coherence. We find that exact resonance ($\nu_1 = \nu_2$) suppresses both ergotropy and charging power due to symmetric thermal population distributions. Introducing finite detuning ($\Delta = \nu_1 - \nu_2$) breaks this symmetry, redistributes populations, and significantly enhances extractable work, charging power, and storage capacity. Furthermore, while the capacity remains invariant under unitary dynamics, providing a useful reference bound, intermediate dipole-dipole coupling strengths ($V_{12}$) optimize the trade-off between ergotropy, coherence retention, and storage performance. Crucially, coherence-assisted energy storage persists up to experimentally relevant temperatures, underscoring the thermal resilience of PBI-based QBs. These results establish spectral detuning and dipole-dipole interaction tuning as essential design principles, positioning PBI dimers as a chemically realistic, experimentally accessible, and thermodynamically robust platform that bridges molecular engineering with quantum energy storage.

quant-ph↗

arXiv2024

Quantum correlations and metrological advantage among Unruh-DeWitt detectors in de Sitter spacetime

A long-standing debate on Gibbons-Hawking (GH) decoherence centers on its unclear thermal nature. In this work, we investigate the robustness of quantum Fisher information (QFI) and local quantum uncertainty (LQU) in the presence of GH decoherence, using free-falling Unruh-DeWitt (UDW) detectors in de Sitter spacetime (dS-ST). The UDW detectors interact with a massless scalar field in dS-ST and are modeled as open quantum systems, with the field acting as the environment for which we use a master equation to describe their evolution. Our analysis investigates the roles of energy spacing, GH temperature, initial state preparation, and various de Sitter-invariant vacuum sectors on the optimization of QFI and LQU. We find that the optimal values of QFI and LQU depend on the selected de Sitter-invariant vacuum sector and increase with larger energy spacing. Our findings reveal that QFI exhibits resilience to GH decoherence, maintaining a pronounced local peak across a wider range of parameters. This robustness can be further enhanced through strategic initial state preparation and increased energy spacing, resulting in a higher maximum QFI value even under significant environmental decoherence. Our results underscore the critical role of GH thermality in governing QFI and LQU, offering valuable insights for advances in relativistic quantum metrology (RQM).

quant-ph↗

arXiv2024

Performance of a Superconducting Quantum Battery

Finding a quantum battery model that demonstrates a quantum advantage while remaining feasible for experimental production is a considerable challenge. Here, a superconducting quantum battery (SQB) model that exhibits such an advantage is introduced. The model consists of two coupled superconducting qubits that interact during the unitary charging process while remaining in equilibrium with a thermal reservoir. First, the model is described, evidence of the quantum advantage is provided, and then the fabrication process of the battery is discussed using superconducting qubits. Analytical expressions for the ergotropy, instantaneous power, and capacity of the SQB, as well as their connection to quantum coherence are derived. It is demonstrated that leveraging the collective effects of Josephson energies and the coupling energy between qubits allows for optimization, resulting in improved energy redistribution and a significant enhancement in charging efficiency. This work highlights the complexities of tuning system parameters, which increase the potential for work extraction from the SQB, providing a deeper understanding of the charging mechanisms involved. These findings can be applied to superconducting quantum circuit battery architectures, underscoring the feasibility of efficient energy storage in these systems. These results pave the way for proposals of new superconducting devices, emphasizing their potential for efficient energy storage.

quant-ph↗

arXiv2024

Kitaev Quantum Batteries: Super-Extensive Scaling of Ergotropy in 1D Spin$-1/2$ $XY-\Gamma(\gamma)$ Chain

We investigate the performance of a novel model based on a one-dimensional (1D) spin-$1/2$ Heisenberg $XY-\Gamma(\gamma)$ quantum chain, also known as 1D Kitaev chain, as a working medium for a quantum battery (QB) in both closed and open system scenarios. We analyze the closed QB scenario by analytically evaluating ergotropy across different spin-spin couplings, anisotropies in spin interactions, Zeeman field strengths, charging field intensities, $\Gamma$ interactions, and temperature. Our results indicate that the ergotropy is highly dependent on spin-spin coupling and anisotropy. Under variable parameters, an increase in the spin-spin coupling strength displays quenches and exhibits non-equilibrium trends in ergotropy. After a quench, ergotropy may experience a sharp increase or drop, suggesting optimal operational conditions for QB performance. In the open QB scenario, we examine spin chains of sizes $2 \leq N \leq 8$ under the influence of dephasing, focusing on the evolution of ergotropy. We study two charging schemes: parallel charging, where spins are non-interacting, and collective charging, involving spin-spin coupling. In the former, increased Zeeman field strength enhances both the peak ergotropy and charging rate, although without any quantum advantage or super-extensive scaling. In the latter, increasing spin-spin coupling might not achieve super-extensive scaling without introducing anisotropy in the spin-spin interaction. Our results suggest that optimal QB performance and a quantum advantage in scaling can be achieved by leveraging anisotropic spin-spin couplings and non-zero $\Gamma$ interactions, allowing for faster charging and higher ergotropy under super-extensive scaling conditions up to $\alpha=1.24$ for the given size of the spin chain.

quant-ph↗

arXiv2024

Magnetic Dipolar Quantum Battery with Spin-Orbit Coupling

We investigate a magnetic dipolar system influenced by the $z$-component of Zeeman splitting, Dzyaloshinsky--Moriya (DM) interaction, and Kaplan--Shekhtman--Entin-Wohlman--Aharony (KSEA) exchange interaction, with emphasis on the role of quantum resources in both closed and open settings. By analyzing the Gibbs thermal state and solving the Lindblad master equation, we study the behavior of quantum coherence, discord, and entanglement under thermal equilibrium and dephasing noise. After exploring these resources, we apply the model to a closed quantum battery (QB). Our results show that while Zeeman splitting degrades quantum resources in noisy and thermal regimes, it enhances QB performance by improving ergotropy, anti-ergotropy, storage capacity, and coherence during cyclic charging. The axial parameter further amplifies performance, leading to coherence saturation and persistent ergotropy growth, in line with the notion of incoherent ergotropy. KSEA interaction and the rhombic term consistently preserve coherence and entanglement under noise, thereby strengthening QB functionality. DM interaction mitigates thermal degradation of resources in the Gibbs state and improves performance, though its effect is limited under Pauli-$X$ dephasing. We reveal diverse behaviors, including increased ergotropy without coherence and the coexistence of coherence with zero extractable work. Finally, we propose Nuclear Magnetic Resonance (NMR) as a feasible platform for experimental implementation.

quant-ph↗

arXiv2024

Quantum obesity and steering ellipsoids for fermionic fields in dilaton black hole

This paper investigates quantum obesity (QO), quantum discord (QD), and the quantum steering ellipsoid (QSE) for bipartite Gisin states subjected to Garfinkle-Horowitz-Strominger (GHS) dilation of spacetime on the second qubit. These three quantifiers are introduced to characterize quantum correlations beyond entanglement and can also function as entanglement witnesses. Our results demonstrate a monotonic decrease in the physical accessibility of both QD and QO as the dilation parameter increases within the region-I of the second qubit. Conversely, in the anti-particle region, the accessibility of QD and QO stabilizes at finite values of the dilation parameter owing to the influence of the Pauli exclusion principle and Fermi-Dirac statistics, subsequently increasing gradually. Notably, the QSE in the region-I expands as the Dirac field frequency rises and the dilation parameter diminishes, while the opposite trend is observed in the anti-particle region.

quant-ph↗

arXiv2024

Physically Accessible and Inaccessible Quantum Correlations of Dirac Fields in Schwarzschild Spacetime

In this study, we investigate the influence of Hawking decoherence on the quantum correlations of Dirac fields between \textit{Alice} and \textit{Bob}. Initially, they share a \textit{Gisin} state near the Schwarzschild black hole (SBH) in an asymptotically flat region. Then, \textit{Alice} remains stationary in this region, while \textit{Bob} hovers near the event horizon (EH) of the SBH. We expect that \textit{Bob}, using his excited detector, will detect a thermal Fermi-Dirac particle distribution. We assess the quantum correlations in the evolved \textit{Gisin} state using quantum consonance and uncertainty-induced non-locality across physically accessible, physically inaccessible, and spacetime regions. Our investigation examines how these measures vary with Hawking temperature, Dirac particle frequency, and the parameters of the initial \textit{Gisin} state. Additionally, we analyze the distribution of these quantum correlation measures across all possible regions, noting a redistribution towards the physically inaccessible region. Our findings demonstrate that Hawking decoherence reduces the quantum correlations of Dirac fields in the physically accessible region, with the extent of reduction depending on the initial state parameters. Moreover, as Hawking decoherence intensifies in the physically inaccessible and spacetime regions, the quantum correlations of Dirac fields reemerge and ultimately converge to specific values at infinite Hawking temperature. These results contribute to our understanding of quantum correlation dynamics within the framework of relativistic quantum information (RQI).

quant-ph↗

arXiv2024

Distribution of distance-based quantum resources outside a radiating Schwarzschild black hole

We obtain analytical expressions for distance-based quantum resources and examine their distribution in the proximity of a Schwarzschild black hole (SBH) within a curved background. For an observer in free fall and their stationary counterpart sharing the Gisin state, the quantum resources are degraded at an infinite Hawking temperature. The extent of this degradation that occurs as the SBH evaporates is contingent upon the fermionic frequency mode, Gisin state parameters, and the distance between the observer and the event horizon (EH). In the case of two accelerating detectors in Minkowski spacetime interacting with quantum fluctuating scalar fields (QFSF), we find that quantum coherence and discord exhibit sudden disappearance for certain initial states and sudden reappearance for others except entanglement, regardless of the Unruh temperature. We also discover that the quantum resources of one detector can be transferred to another in the case of two stationary detectors through a fluctuating quantum field outside the SBH. We demonstrate that, in contrast to coherence and discord, we are unable to regenerate entanglement for a given initial state and that they are equal for different vacuum states. In certain circumstances, the presence of EHs does not significantly reduce the available resources, as it turns out that all interesting phenomena occur within EHs. Since the world is basically non-inertial, it is necessary to understand the distribution of quantum resources within a relativistic framework.

quant-ph↗