arXiv subjects

Rachid Ahl Laamara

Publications and source records attributed to Rachid Ahl Laamara.

At least 55 records · Page 3Linked to original sources

arXiv2025

Multiparticle Quantum Heat Engine: Exploring the Impact of Criticality on Efficiency

Quantum many-body systems present substantial technical challenges from both analytical and numerical perspectives. Despite these difficulties, some progress has been made, including studies of interacting atomic gases and interacting quantum spins. Furthermore, the potential for criticality to enhance engine performance has been demonstrated, suggesting a promising direction for future investigation. Here, we explore the performance of a quantum Otto cycle using a long-range Ising chain as the working substance. We consider an idealized cycle consisting of two adiabatic transformations and two perfect thermalizations, eliminating dissipation. Analyzing both engine and refrigerator modes, we investigate the influence of particle number, varied from 10 to 100, on efficiencies and behavior near the critical point of the phase transition, which we characterize using a scaling factor. We also examine how internal factors; specifically, the power-law exponent, the number of particles, and the hot and cold reservoir temperatures, affect the system's operation in different modes. Our results reveal that these factors have a different impact compared to their classical counterparts.

quant-ph↗

arXiv2025

Holographic F(Q,T) Gravity with Lambert Solution

In this work, we study a model of holographic dark energy using FLRW cosmology in the context of modified gravity. An extension of the symmetric teleparallel gravity is obtained by considering the gravitational action L is given by an arbitrary function f of the nonmetricity Q, where the nonmetricity Q is responsible for the gravitational interaction, and the trace of the matter energy momentum tensor T, so that L=f(Q,T). We expand on the features of the derived cosmological model in view of the relation between cosmic time and redshift as t(z)=kt0/b*f(z) where f(z) = W[b/k*e((b-ln(1+z))/k)] and W denotes the Lambert function, and discuss the evolution of the trajectories of the equation of state parameters and deceleration parameter in the evolving universe using a special then generalized version of the model.

gr-qc↗

arXiv2025

Dynamics of Linear Scalar Perturbation in f(Q)+f(T) class of f(Q,T) gravity

In this work, we study the f(Q,T) model of symmetric teleparallel modified gravity in the framework of cosmological perturbation theory. Using a general approach, we extract the differential matter density equation then we simplify it as a second-order equation by considering the sub-Hubble approximation. Our analysis is then based on two different forms of f(Q,T) that we study in a classic approach and again using Holographic dark energy. Our initial results yield a significant divergence from the perturbed behavior of the LambdaCDM model, imposing stringent constraints on the feasibility of this class of theories but the HDE contribution triggers an interesting discussion.

gr-qc↗

arXiv2025

Quantifying non-Markovianity via local quantum Fisher information

Characterizing non-Markovianity in open quantum systems (OQSs) is gaining increasing attention due to its profound implications for quantum information processing. This phenomenon arises from the system's evolution being influenced by its previous interactions with the environment. To better understand these complex dynamics, various measures have been proposed, including those based on divisibility, quantum mutual information, and trace distance. Each of these measures provides a different perspective on the behavior of OQSs. Here, we introduce a novel approach to quantifying non-Markovianity by focusing on metrological non-classical correlations. This approach is based on a discord-like measure of quantum correlations for multi-component quantum systems known as local quantum Fisher information (LQFI), which was introduced in [58]. It is defined as the minimization of quantum Fisher information with respect to local observables and measurements. Thereby, we examine some examples to clarify the use of our metric by applying it to three different channels: the phase damping channel, the amplitude damping channel, and the depolarizing channel. In contrast to other approaches, this new metric focuses on correlated bipartite $2\otimes d$ systems, has a clear physical interpretation, and effectively captures the features of non-Markovianity. We demonstrate that the non-Markovian or Markovian evolution of an open correlated bipartite system corresponds to an increase or decrease, respectively, in the quantumness of the quantum state. This quantumness is quantified by the maximum of the measurement-induced Fisher information across all local von Neumann measurements. Compared to measuring non-Markovianity based on local quantum uncertainty, a measure of non-classical correlation of the discord type based on single observables, our results confirm that the ..

quant-ph↗

arXiv2025

Characterizing non-Markovianity via quantum coherence based on Kirkwood-Dirac quasiprobability

We present a new measure of non-Markovianity based on the property of nonincreasing quantum coherence via Kirkwood-Dirac (KD) quasiprobability under incoherent completely positive trace-preserving maps. Quantum coherence via the KD quasiprobability is defined as the imaginary part of the KD quasiprobability, which is maximised over all possible second bases and evaluated using an incoherent reference basis. A measure non-Markovianity based on KD quasiprobability coherence would capture memory effects via the time evolution of the imaginary part of the KD quasiprobability, providing an experimentally accessible and physically intuitive alternative to traditional measures relying on quantum Fisher information or trace distance. This approach is applied to the study of dissipation and dephasing dynamics in single- and two-qubit systems. The results obtained show that, in the cases studied, our measure based on coherence via Kirkwood-Dirac quasiprobability performs at least as well as $\ell_{1}$-norm coherence in detecting non-Markovianity, this provides a novel perspective on the analysis of non-Markovian dynamics.

quant-ph↗

arXiv2025

Extracted work as measure of entanglement in optomechanics

In this work, we investigate quantum entanglement and work extraction in two distinct optomechanical systems. The first system consists of two spatially separated Fabry-Pérot cavities driven by squeezed light in the resolved-sideband regime, while the second system comprises a laser field incident on a vibrating mirror. We analyze the entanglement dynamics between optical and mechanical modes, as well as quantum correlations in a mixed optomechanical bipartite system (optic-optic mode) mediated by radiation pressure. Using logarithmic negativity as a measure, we quantify the entanglement evolution in both optic-optic and mirror-mirror bipartite subsystems. Furthermore, we show how three distinct types of extractable work vary with system parameters and examine their relationship with entanglement. Our results highlight the relationship between quantum correlations and extracted work in optomechanical system, offering insights for quantum information processing and energy transfer in hybrid systems.

quant-ph↗

arXiv2025

Multiple phase estimation with photon-added multi-mode coherent states of GHZ-type

This paper explores multiparameter quantum metrology using Greenberger-Horne-Zeilinger (GHZ)-type photon-added coherent states (PACS) and investigates both independent and simultaneous parameter estimation with linear and non-linear protocols, highlighting the significant potential of quantum resources to enhance precision in multiparameter scenarios. To provide a comprehensive analysis, we explicitly derive analytical expressions for the quantum Cramér-Rao bound (QCRB) for each protocol. Additionally, we compare the two estimation strategies, examining the behavior of their QCRBs and offering insights into the advantages and limitations of these quantum states in various contexts. Our results show that simultaneous estimation generally outperforms independent estimation, particularly in non-linear protocols. Furthermore, we analyze how the QCRB varies with the coherent state amplitude $|α|^2$, the number of estimated parameters $d$, and the photon excitation order $n$ across three protocols. The results indicate that increasing $|α|^2$ and decreasing $d$ improves estimation precision. For low $n$, the variation in the QCRB is similar for both symmetric and antisymmetric cases; however, at higher $n$, the antisymmetric case exhibits slightly better precision. The dependence on $d$ is comparable for both types of states. We also compare PACS-based GHZ states with NOON states and entangled coherent states, demonstrating the relative performance of each. Finally, we conclude with an analysis of homodyne detection in the context of a linear protocol, discussing its impact on estimation accuracy.

quant-ph↗

arXiv2025

Quantum synchronization and entanglement of two magnon modes in a magnomechanical system

We investigate theoretically the improvement of the entanglement between the indirectly coupled two magnon modes in a magnomechanical system with magnon squeezing. We quantify the degree of entanglement via logarithmic negativity between two magnon modes. We show a significant enhancement of entanglement via magnon squeezing. Additionally, the entanglement of two magnons decreases monotonically under thermal effects. We demonstrate that with an increasing photon tunneling rate, entanglement is robust and resistant to thermal effects. We use purity as a witness to the mixing between the two magnon modes. We show that synchronization and purity are very robust against thermal effects rather than entanglement. We examine the relationship between quantum entanglement, purity, and quantum synchronization in both steady and dynamic states. According to our results, this scheme could be a promising platform for studying macroscopic quantum phenomena.

quant-ph↗

arXiv2025

Constructing Multipartite Planar Maximally Entangled States from Phase States and Quantum Secret Sharing Protocol

In this paper, we explore the construction of Planar Maximally Entangled (PME) states from phase states. PME states form a class of $n$-partite states in which any subset of adjacent particles whose size is less than or equal to half the total number of particles is in a fully entangled state. This property is essential to ensuring the robustness and stability of PME states in various quantum information applications. We introduce phase states for a set of so-called noninteracting $n$ particles and describe their corresponding separable density matrices. These phase states, although individually separable, serve as a starting point for the generation of entangled states when subjected to unitary dynamics. Using this method, we suggest a way to make complex multi-qubit states by watching how unconnected phase states change over time with a certain unitary interaction operator. In addition, we show how to derive PME states from these intricate phase states for two-, three-, four-, and K-qubit systems. This construction method for PME states represents a significant advance over absolutely maximally entangled (AME) states, as it provides a more accessible and versatile resource for quantum information processing. Not only does it enable the creation of a broader class of multipartite entangled states, overcoming the limitations of AME states, notably their restricted availability in low-dimensional systems; for example, the absence of a four-qubit AME state, but it also offers a systematic construction method for any even number of qudits, paving the way for practical applications in key quantum technologies such as teleportation, secret sharing and error correction, where multipartite entanglement plays a central role in protocol efficiency.

quant-ph↗

arXiv2025

Unlocking thermodynamic multitasking: Exploring the functioning of two-qubit engines through coherence and entanglement

Recent studies have investigated the role of entanglement in the operation of a two-qubit system as a heat engine, showing that work can be extracted from a single heat bath without direct heat dissipation between the two-qubit system and the cold bath (2021 Phys. Rev. Lett, 126, 120605). In this work, we explore the impact of operating the same two-qubit system model with two heat baths and direct dissipation to the environment by applying both a local and a global Markovian master equation. The addition of a second heat bath enables the system to operate in different modes depending on the initial quantum state. We examine the temporal behavior of concurrence entanglement and quantum coherence, analyzing their observable roles in transitions between various operational regimes. Additionally, we investigate the evolution of information flow throughout the working cycle of the two-qubit system, focusing on the influence of individual and collective decoherence on the system's efficiency and operational modes. We identify the optimal parameter regions for the engine and refrigerator modes to achieve maximum performance. Finally, we investigate the effect of coherence outside the system on its thermodynamic quantities.

quant-ph↗

arXiv2025

Enhancing phase sensitivity in Mach-Zehnder interferometer with various detection schemes using SU(1,1) coherent states

Improving interferometric phase sensitivity is crucial for high-precision measurements in rapidly developing quantum technologies. The Mach-Zehnder interferometer (MZI) is a versatile tool for analyzing this phenomenon. By splitting and recombining a light beam using beam splitters, MZIs allow for precise phase sensitivity analysis using tools like the quantum Cramér-Rao bound (QCRB) and the quantum Fisher information (QFI). This paper analyzes the phase sensitivity of a MZI in various scenarios using different detection schemes and input states. We compare the single- and two-parameter quantum estimation and their associated QCRB for three phase-shift situations: in both arms, only in the upper arm (asymmetric), and in both arms symmetrically. We then investigate the phase sensitivity under three detection schemes: intensity difference, single-mode intensity, and balanced homodyne. Additionally, we explore the use of Perelomov and Barut-Girardello coherent states, two types of SU(1,1) coherent states, in all scenarios. Notably, we demonstrate that under optimal conditions, all detection schemes can achieve the QCRB by utilizing SU(1,1) coherent states as input states.

quant-ph↗

arXiv2024

Quantum phase estimation and realistic detection schemes in Mach-Zehnder interferometer using SU(2) coherent states

In quantum parameter estimation, the quantum Cramér-Rao bound (QCRB) sets a fundamental limit on the precision achievable with unbiased estimators. It relates the uncertainty in estimating a parameter to the inverse of the quantum Fisher information (QFI). Both QCRB and QFI are valuable tools for analyzing interferometric phase sensitivity. This paper compares the single-parameter and two-parameter QFI for a Mach-Zehnder interferometer (MZI) with three detection schemes: single-mode and difference intensity detection, neither has access to an external phase reference and balanced homodyne detection with access to an external phase reference. We use a spin-coherent state associated with the su(2) algebra as the input state in all scenarios and show that all three schemes can achieve the QCRB for the spin-coherent input state. Furthermore, we explore the utilization of SU(2) coherent states in diverse scenarios. Significantly, we find that the best pressure is obtained when the total angular momentum quantum number $j$ is high, and we demonstrate that given optimal conditions, all detection schemes can achieve the QCRB by utilizing SU(2) coherent states as input states.

quant-ph↗

arXiv2024

Parity symmetry breaking of spin-$j$ coherent state superpositions in Gaussian noise channel

The Wigner function and Wigner-Yanase skew information are connected through quantum coherence. States with high skew information often exhibit more pronounced negative regions in their Wigner functions, indicative of quantum interference and non-classical behavior. Thus, the relationship between these two concepts is that states with high quantum coherence tend to display more non-classical features in their Wigner functions. By exploiting this relationship, which manifests as parity symmetry and asymmetry, we analyze parity symmetry and asymmetry in the superposition of two spin coherent states for a spin-$1/2$, as well as for a general spin-$j$. This analysis shows that the preservation of the parity asymmetry, or the violation of the parity symmetry, correlates with an increase in the value of spin $j$. Additionally, we investigate the behavior of parity symmetry and asymmetry of these states subjected to a Gaussian noise channel. Specifically, we examine how this parity symmetry and asymmetry change and identify the points at which parity symmetry is violated in the spin-$1/2$ cat state. Notably, the violation of parity symmetry becomes more pronounced at higher values of the decoherence parameter $s$. Our study shows how the spin value $j$ affects the breaking of parity symmetry in general spin-$j$ cat states that are hit by Gaussian noise.

quant-ph↗

arXiv2024

Higher spin AdS$_{3}$ gravity and Tits-Satake diagrams

We investigate higher spin AdS$_{3}$ gravity with real split forms of complex A$_{N}$ B$_{N}$, C$_{N}$ and D$_{N}$ Lie algebras. This is done by linking $SO(1,2)$ spin multiplets with splitted root systems using Tits-Satake diagrams of real forms. Unlike $SL(N,R)$, we show that the orthogonal families have two different higher spin (HS) spectrums: vectorial and spinorial. We find amongst others that the spinorial spectrum has an isolated spin j$_{\mathcal{N}}$ given by $\mathcal{N}\left(\mathcal{N}+1\right)/2$ for $SO(\mathcal{N},1+\mathcal{N})$ and $\mathcal{N} \left( \mathcal{N}-1\right) /2$ for $SO(\mathcal{N},\mathcal{N})$. We implement these results into the computation of the HS partition functions in these gravity theories and identify the individual contributions of the higher spin fields; valuable to manoeuver the HS-BTZ black hole partition function

hep-th↗

arXiv2024

Enhancing One-Way Steering and Non-Classical Correlations in Magnomechanics via Coherent Feedback

In this work, we propose a theoretical scheme to explore the enhancement of quantum correlation hierarchies in a cavity magnonmechanical system via the coherent feedback tool. We use Gaussian geometric discord to quantify quantum correlations between the two magnon modes, including those beyond entanglement, in the steady state. Logarithmic negativity and Gaussian quantum steering are employed to characterize entanglement and steerability, respectively. Our results show that adjusting the beam splitter's reflective parameter can significantly enhance quantum correlations and increase their resilience to thermal noise. Moreover, we demonstrate that coherent feedback can achieve enhanced genuine tripartite entanglement among the photon, magnon $M_1$, and phonon. These findings present promising strategies for enhancing entanglement in magnon-based systems and advancing quantum information technologies. We conclude by validating the system and demonstrating its ability to detect entanglement.

quant-ph↗

arXiv2024

Achieving quantum metrological performance and exact Heisenberg limit precision through superposition of $s$-spin coherent states

In quantum phase estimation, the Heisenberg limit provides the ultimate accuracy over quasi-classical estimation procedures. However, realizing this limit hinges upon both the detection strategy employed for output measurements and the characteristics of the input states. This study delves into quantum phase estimation using $s$-spin coherent states superposition. Initially, we delve into the explicit formulation of spin coherent states for a spin $s=3/2$. Both the quantum Fisher information and the quantum Cramer-Rao bound are meticulously examined. We analytically show that the ultimate measurement precision of spin cat states approaches the Heisenberg limit, where uncertainty decreases inversely with the total particle number. Moreover, we investigate the phase sensitivity introduced through operators $e^{iζ{S}_{z}}$, $e^{iζ{S}_{x}}$ and $e^{iζ{S}_{y}}$, subsequently comparing the resultants findings. In closing, we provide a general analytical expression for the quantum Cramer-Rao boundary applied to these three parameter-generating operators, utilizing general $s$-spin coherent states. We remarked that attaining Heisenberg-limit precision requires the careful adjustment of insightful information about the geometry of $s$-spin cat states on the Bloch sphere. Additionally, as the number of $s$-spin increases, the Heisenberg limit decreases, and this reduction is inversely proportional to the $s$-spin number.

quant-ph↗

arXiv2024

Superspin Chains Solutions from 4D Chern-Simons Theory

As a generalisation of the correspondence linking 2D integrable systems with 4D Chern-Simons (CS) gauge theory, superspin chains are realized by means of crossing electric and magnetic super line defects in the 4D CS with super gauge symmetry. The oscillator realization of Lax operators solving the RLL relations of integrability is obtained in the gauge theory by extending the notion of Levi decomposition to Lie superalgebras. Based on particular 3-gradings of Lie superalgebras, we obtain graded oscillator Lax matrices for superspin chains with internal symmetries given by $A(m-1\mid n-1)$, $B(m\mid n)$, $C(n)$ and $D(m\mid n)$

hep-th↗

arXiv2024

Simulating the Quantum Rabi Model in Superconducting Qubits at Deep Strong Coupling

The Quantum Rabi model serves as a pivotal theoretical framework for elucidating the nuanced interplay between light and matter. Utilizing circuit quantum electrodynamics on a chip, we address the challenge of achieving deep strong coupling in Quantum Cavity Electrodynamics (cQED). Despite progress in superconducting circuits and trapped ions, experimental realization has been limited to spectroscopy. Our focus is on a transformative digital quantum simulation, employing Trotterization with an augmented number of steps to deconstruct a complex unitary Hamiltonian. This approach showcases the benefits of digital techniques within superconducting circuits, offering universality, flexibility, scalability, and high fidelity. Our goal is to demonstrate deep strong coupling in cQED and understand the advantages of digital methods, particularly in coherent measurement during time evolution with varying photon counts in resonators. This opens avenues to leverage quantum mechanics for overcoming hardware limitations.

quant-ph↗