arXiv subjects

Saeed Haddadi

Publications and source records attributed to Saeed Haddadi.

At least 37 records · Page 2Linked to original sources

arXiv2026

Phase-Driven Precision Boost in Quantum Compression for Postselected Metrology

We reveal the noncyclic Pancharatnam phase--arising from the coherent system-meter interaction--as a fundamental criterion that governs the optimal performance of quantum compression channels in postselected metrology. This phase embodies a geometric connection that enables precise control over the parallel evolution of the meter state, thereby maximizing the quantum Fisher information per trial and achieving lossless compression channels. Remarkably, fine-tuning the postselection parameter just below this optimal phase incurs substantial information loss, whereas tuning it just above fully suppresses undesired parallel evolution, enhancing information retention beyond that achievable in postselected protocols lacking Pancharatnam phase effects. We further reveal that leveraging qudit meter states can unlock a substantial additional enhancement. These findings establish the Pancharatnam phase as a geometric benchmark, guiding the design of high-precision quantum parameter estimation protocols.

quant-ph↗

arXiv2025

Gravitational cat states as a resource for quantum information processing

We investigate how resourceful gravitational cat states are to preserve quantum correlations. In this regard, we explore the dynamics of gravitational cat states under different situations such as thermal, classical stochastic, general decaying, and power-law noisy fields. In particular, the one-way steerability, Bell non-locality, entanglement, and purity in two qubits are our main focus. We also address the weak measurement protocol on the dynamics of quantum correlations and purity of the state. Our results show that the gravitational cat states have a reliable and better capacity to preserve quantum correlations and remain one of the good resources for the deployment of quantum information processing protocols. Additionally, two independent channels are also employed and it is observed that only the weaker coupling regimes are effective in preserving quantum correlations. Notably, in terms of non-Markovian dynamics implication, quantum correlations are found to be longer preserved because of the information feedback phenomenon between the system and environment. Finally, we present a brief analysis to extend our gravitational model to include the electrostatic notion, providing insight into the key differences between the considered configurations.

quant-ph↗

arXiv2025

Coherence, Transport, and Chaos in 1D Bose-Hubbard Model: Disorder vs. Stark Potential

Quantum coherence and phase transitions are studied in a finite one-dimensional Bose--Hubbard model using exact diagonalization under thermal fluctuations, a Stark potential, and disorder. The condensate fraction, superfluid fraction, visibility, number fluctuations, and the $\ell_1$-norm of coherence are computed to characterize the Mott insulator--superfluid transition. Although finite-size effects prevent a sharp transition, ground-state properties reveal signatures of quantum criticality. Thermal fluctuations can enhance coherence via tunneling, a Stark potential promotes localization, and disorder suppresses global superfluidity while preserving local coherence. These results highlight how disorder, tilt, and temperature reshape coherence and offer insights for quantum simulation and strongly correlated phases. For systems up to six sites with unit filling, a spectral analysis is also performed through the metric mean gap ratio (MGR). However, limited statistics due to the small system size and computational constraints prevent a complete characterization of quantum chaos, yielding only approximate signatures.

cond-mat.quant-gas↗

arXiv2025

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↗

arXiv2025

Quantum correlations versus spin magnitude: Transition to the classical limit

Quantum-classical transitions have long attracted much attention. We study such transitions in quantum spin-($j$,1/2) systems at thermal equilibrium. Unlike the previous work [Phys. Rev. A 73, 064302 (2006)], it is found that the threshold temperature of quantum entanglement decreases with increasing spin $j$ and completely disappears in the limit $j\to\infty$. In the ground state of systems with highly symmetric interactions, the discord-type quantum correlations can exist even for arbitrarily large spin. Such correlations turn out to be unstable and are destroyed by small perturbations that violate the symmetry of the Hamiltonian. The stable quantum correlations gradually degrade as the spin $j$ grows and eventually vanish when the classical limit is reached.

quant-ph↗

arXiv2025

Single-photon emission modeling with statistical estimators for the exponential distribution

Single-photon sources are used in numerous quantum technologies, from sensing and imaging to communication, making the accurate modeling of their emissions essential. In this work, we propose a statistical framework for describing single-photon emission processes and implement estimators for the exponential distribution to quantify this phenomenon. Our approach provides a reliable method for estimating the radiative decay time, represented by the inverse rate parameter, which is crucial in quantum optics applications. We explore several statistical estimators, including maximum likelihood estimation, minimum-variance unbiased estimator, and best linear unbiased estimator. To validate our theoretical methods, we test the proposed estimators on experimental data, demonstrating their applicability in real-world settings. We also evaluate the performance of these estimators when dealing with censored data, a frequent limitation in photon emission experiments. The analysis allows us to track the performance of the proposed estimators as the amount of available data decreases, providing insights into their reliability for modeling single-photon emission events under limited resources.

quant-ph↗

arXiv2025

Quantum correlations in general qubit-qudit axially symmetric states

The development and improvement of analytical methods for evaluating nonclassical correlations is one of the most important tasks in quantum information science. In this paper, we investigate a mixed spin-$(1/2,S)$ system with an arbitrary spin $S$, where the interactions satisfy the U(1) axial symmetry. Analytical formulas for the local quantum uncertainty (LQU) and local quantum Fisher information (LQFI) are derived directly from the elements and eigenvalues of the density matrix. These results are then used to conduct a comparative analysis of the discord-like quantum correlations, LQU and LQFI, in the system at thermal equilibrium. The high-temperature asymptotics of both quantum correlations are found explicitly. Despite the destructive role of temperature in general, the calculations show that the quantum correlations can increase with temperature in local intervals. Under certain conditions, temperature even generates quantum correlations from uncorrelated ground states. Further, as the system cools, quantum correlations can undergo a series of abrupt transitions with a smooth temperature change. These phenomena are demonstrated for different choices of coupling parameters and spin lengths $S$.

quant-ph↗

arXiv2025

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↗

arXiv2025

Jahn-Teller Effect for Controlling Quantum Correlations in Hexanuclear Fe$^{3+}$ Magnets

We investigate the low-temperature magnetic and quantum properties of hexanuclear Fe$^ {3+}_6$ complexes under an external magnetic field. We primarily study the impact of competing exchange interactions and their asymmetries induced by the Jahn-Teller distortion on the quantum properties of the complexes. The inequality in exchange interactions lifts the ground-state degeneracy that gives rise to complex quantum behavior. By constructing the ground-state phase diagram and analyzing magnetization, we identify key magnetic phases and critical phenomena. We further quantify quantum correlations using tripartite entanglement negativity and conditional von Neumann entropy to unveil how the Jahn-Teller effect enhances intra-triangle entanglement while modulating inter-triangle correlations. Our findings highlight the Fe$^{3+}_6$ complex as a promising molecular platform for tunable quantum correlations, with potential applications in quantum information processing and molecular qubits.

cond-mat.mtrl-sci↗

arXiv2025

Quantum Information Resources in Spin-1 Heisenberg Dimer Systems

We explore the quantum information resources within bipartite pure and mixed states of the quantum spin-1 Heisenberg dimer system, considering some interesting factors such as the $l_{1}$-norm of quantum coherence, relative coherence, negativity, and steering, influenced by the magnetic field and uniaxial single-ion anisotropy. Through a thorough investigation, we derive the system's density operator at thermal equilibrium and establish a mathematical framework for analyzing quantum resource metrics. Our results unveil the system's behavior at absolute zero temperature. We further observe temperature's role in transitioning the system towards classical states, impacting coherence, entanglement, and steering differently. Notably, we find that increasing the exchange anisotropy parameter can reinforce quantum correlations while adjusting the uniaxial single-ion anisotropy influences the system's quantumness, particularly when it is positive. Some recommendations to maximize quantum coherence, entanglement, and steering involve temperature reduction, increasing the exchange anisotropy parameter, and carefully managing the magnetic field and uniaxial single-ion anisotropy parameter, highlighting the intricate interplay between these factors in maintaining the system's quantum properties.

quant-ph↗

arXiv2025

A comparative study of LQU and LQFI in general qubit-qutrit axially symmetric states

We derive the compact closed forms of local quantum uncertainty (LQU) and local quantum Fisher information (LQFI) for hybrid qubit-qutrit axially symmetric (AS) states. This allows us to study the quantum correlations in detail and present some essentially novel results for spin-(1/2, 1) systems, the Hamiltonian of which contains ten independent types of physically important parameters. As an application of the derived formulas, we study the behavior of these two quantum correlation measures at thermal equilibrium. New features are observed in their behavior that are important for quantum information processing. Specifically, cascades of sudden changes in the behavior of LQU and LQFI are found with a smooth change in temperature or interaction parameters. Interestingly, in some cases, sudden transitions are observed in the behavior of LQU but not in LQFI, and vice versa. Moreover, our compact formulas open a way to apply them to other problems, for instance, when investigating the environmental effects on quantum correlations in open systems.

quant-ph↗

arXiv2025

Molecular Nanomagnet $\text{Cu}^\text{II}\text{Ni}^\text{II}\text{Cu}^\text{II}$ as Resource for Bipartite and Tripartite Quantum Entanglement and Coherence

We investigate key quantum characteristics of the mixed spin-(1/2,1,1/2) Heisenberg trimer under the influence of an external magnetic field. Specifically, we analyze the distributions of bipartite and tripartite entanglement quantified through the respective negativities, and the $l_1$-norm of coherence with the help of rigorous analytical and numerical methods. Our findings suggest that the heterotrinuclear molecular nanomagnet $[\{\text{Cu}^\text{II}\text{L}\}_2\text{Ni}^\text{II}(\text{H}_2\text{O})_2](\text{ClO}_4)_{2} . 3\text{H}_2\text{O}$, which represents an experimental realization of the mixed spin-(1/2,1,1/2) Heisenberg trimer, exhibits a significant bipartite entanglement between $\text{Cu}^\text{II}$ and $\text{Ni}^\text{II}$ magnetic ions along with robust tripartite entanglement among all three constituent $\text{Cu}^\text{II}\text{Ni}^\text{II}\text{Cu}^\text{II}$ magnetic ions. The significant bipartite and tripartite entanglement persists even at relatively high temperatures up to $37\,\text{K}$ and magnetic fields up to $46\,\text{T}$, whereby the coherence is maintained even at elevated temperatures. {It is evidenced that the aforementioned molecular complex with the magnetic core $\text{Cu}^\text{II}\text{Ni}^\text{II}\text{Cu}^\text{II}$ provides an intriguing quantum resource, which exhibits a star-shaped state within the singlet eigenstate at low magnetic fields and W-like state within the triplet eigenstate at moderate magnetic fields.

quant-ph↗

arXiv2024

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

We investigate the performance of a novel model based on a one-dimensional (1D) spin-$1/2$ Heisenberg $XY-Γ(γ)$ 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, $Γ$ 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 $Γ$ interactions, allowing for faster charging and higher ergotropy under super-extensive scaling conditions up to $α=1.24$ for the given size of the spin chain.

quant-ph↗

arXiv2024

Tripartite measurement uncertainty in Schwarzschild space-time

The effect of Hawking radiation on tripartite measurement uncertainty in a Schwarzschild black hole background is analyzed in this study. Two scenarios are examined. In the first, quantum memory particles approach a Schwarzschild black hole and are positioned near the event horizon, while the particle being measured remains in the asymptotically flat region. In the second scenario, the measured particle moves toward the black hole, and the quantum memories stay in the asymptotically flat region. This study considers two initial quantum states, namely GHZ and W states. Our findings reveal that in both cases, measurement uncertainty increases steadily with rising Hawking temperature. When comparing the GHZ and W states, the GHZ state initially exhibits lower measurement uncertainty at low Hawking temperatures than the W state, indicating greater resilience to Hawking radiation. Additionally, when the quantum memories remain in the asymptotically flat region while the measured particle falls toward the black hole, the uncertainties for GHZ and W states do not align at high temperatures. The GHZ state consistently demonstrates lower measurement uncertainty, showcasing its superior robustness against Hawking radiation.

gr-qc↗

arXiv2024

Ergotropy and capacity optimization in Heisenberg spin-chain quantum batteries

This study examines the performance of finite spin quantum batteries (QBs) using Heisenberg spin models with Dzyaloshinsky-Moriya (DM) and Kaplan--Shekhtman--Entin-Wohlman--Aharony (KSEA) interactions. The QBs are modeled as interacting quantum spins in local inhomogeneous magnetic fields, inducing variable Zeeman splitting. We derive analytical expressions for the maximal extractable work, ergotropy and the capacity of QBs, as recently examined by Yang et al. [Phys. Rev. Lett. 131, 030402 (2023)]. These quantities are analytically linked through certain quantum correlations, as posited in the aforementioned study. Different Heisenberg spin chain models exhibit distinct behaviors under varying conditions, emphasizing the importance of model selection for optimizing QB performance. In antiferromagnetic (AFM) systems, maximum ergotropy occurs with a Zeeman splitting field applied to either spin, while ferromagnetic (FM) systems benefit from a uniform Zeeman field. Temperature significantly impacts QB performance, with ergotropy in the AFM case being generally more robust against temperature increases compared to the FM case. Incorporating DM and KSEA couplings can significantly enhance the capacity and ergotropy extraction of QBs. However, there exists a threshold beyond which additional increases in these interactions cause a sharp decline in capacity and ergotropy. This behavior is influenced by temperature and quantum coherence, which signal the occurrence of a sudden phase transition. The resource theory of quantum coherence proposed by Baumgratz et al. [Phys. Rev. Lett. 113, 140401 (2014)] plays a crucial role in enhancing ergotropy and capacity. However, ergotropy is limited by both the system's capacity and the amount of coherence. These findings support the theoretical framework of spin-based QBs and may benefit future research on quantum energy storage devices.

quant-ph↗

arXiv2024

Optimizing QKD efficiency by addressing chromatic dispersion and time measurement uncertainty

In this paper, we present a Quantum Key Distribution (QKD) protocol that accounts for fundamental practical challenges, including chromatic dispersion, time measurement uncertainty, and dark counts. Our analysis provides a comprehensive framework for understanding the impact of these physical phenomena on QKD efficiency, offering practical strategies for enhancing the robustness and security of quantum communication systems in real-world applications. In particular, by manipulating the chirp parameter of single-photon wave packets, we demonstrate significant improvements in key generation rates and an extended range of secure communication.

quant-ph↗

arXiv2024

Effects of Chromatic Dispersion on Single-Photon Temporal Wave Functions in Quantum Communications

In this study, we investigate the effects of chromatic dispersion on single-photon temporal wave functions (TWFs) in the context of quantum communications. Departing from classical beam analysis, we focus on the temporal shape of single photons, specifically exploring generalized Gaussian modes. From this foundation, we introduce chirped and unchirped Gaussian TWFs, demonstrating the impact of the chirp parameter in mitigating chromatic dispersion effects. Furthermore, we extend our investigation to time-bin qubits, a topic of ongoing research relevance. By exploring the interplay of dispersion effects on qubit interference patterns, we contribute essential insights to quantum information processing. This comprehensive analysis considers various parameters, introducing a level of complexity not previously explored in the context of dispersion management. We demonstrate the relationships between different quantities and their impact on the spreading of TWFs. Our results not only deepen the theoretical understanding of single-photon TWFs but also offer practical guidelines for system designers to optimize symbol rates in quantum communications.

quant-ph↗

arXiv2024

A Study on Thermal Quantum Resources and Probabilistic Teleportation in Spin-1/2 Heisenberg XYZ+DM+KSEA Model under Variable Zeeman Splitting

We investigate the behavior of various measures of quantum coherence and quantum correlation in the spin-1/2 Heisenberg XYZ model with added Dzyaloshinsky-Moriya (DM) and Kaplan--Shekhtman--Entin-Wohlman--Aharony (KSEA) interactions at a thermal regime described by a Gibbs density operator. We aim to understand the restricted hierarchical classification of different quantum resources, where Bell nonlocality $\subseteq$ quantum steering $\subseteq$ quantum entanglement $\subseteq$ quantum discord $\subseteq$ quantum coherence. This hierarchy highlights the increasingly stringent conditions required as we move from quantum coherence to more specific quantum phenomena. In order to enhance quantum coherence, quantum correlation, and fidelity of teleportation, our analysis encompasses the effects of independently provided sinusoidal magnetic field control as well as DM and KSEA interactions on the considered system. The results reveal that enhancing the entanglement or quantum correlation of the channel does not always guarantee successful teleportation or even an improvement in teleportation fidelity. Thus, the relationship between teleportation fidelity and the channel's underlying quantum properties is intricate. Our study provides valuable insights into the complex interplay of quantum coherence and correlation hierarchy, offering potential applications for quantum communication and information processing technologies.

quant-ph↗