arXiv subjects

Md. Manirul Ali

Publications and source records attributed to Md. Manirul Ali.

At least 19 recordsLinked to original sources

arXiv2026

Robustness of Quantum Discord in Nonequilibrium Electronic Transport through Tunnel-Coupled Quantum Dots

Quantum discord captures quantum correlations beyond entanglement and can remain finite even when the entanglement vanishes. We investigate the transient nonequilibrium dynamics and steady-state behavior of quantum discord and classical correlations in a double quantum dot (DQD) system coupled to fermionic reservoirs. By employing a quantum Langevin equation formalism, we obtain the exact reduced density matrix of the system, enabling a comprehensive analysis of its quantum and classical correlations under nonequilibrium conditions. The influence of system-reservoir coupling strength, spectral bandwidth, thermal bias, and varying initial state on both the transient dynamics and steady-state correlations is systematically analyzed. Quantum discord remains finite in the nonequilibrium steady state over a broad parameter range. Although thermal gradients reduce the overall magnitude of correlations, quantum discord persists and exhibits greater resilience. These results demonstrate that nonequilibrium electronic transport, together with the environmental spectral properties and reservoir asymmetry, provides an effective means of controlling nonclassical correlations in mesoscopic systems and establishes quantum discord as a robust hallmark of open fermionic quantum devices.

cond-mat.mes-hall↗

arXiv2025

Non-maximally entangled mixed states of X and non-X types as teleportation channels

Mixed spin-1/2 states violating Bell-CHSH inequality is useful for teleportation. There exist states which do not violate Bell-inequality but is still useful as teleportation channels. Maximally entangled mixed states of Munro class and Ishizaka-Hiroshima class are such types which although satisfy Bell-CHSH inequality, yet can perform better as teleportation channels for a given degree of mixedness\cite{adhikari2010}. In this work we construct class of mixed states of non-maximally entangled types whose efficacy as teleportation channels have been studied. For certain range of state parameters, these non-maximally entangled mixed states performs better as quantum teleportation channels than certain maximally entangled mixed states (such as Werner state). These constructed states, though entangled, satisfy Bell-CHSH inequality implying further that violation of local inequalities may not be good indicators of their ability to complete quantum processing tasks such as teleportation.

quant-ph↗

arXiv2025

Exploring quantum properties of bipartite mixed states under coherent and incoherent basis

Quantum coherence and quantum entanglement are two different manifestations of the superposition principle. In this article we show that the right choice of basis to be used to estimate coherence is the separable basis. The quantum coherence estimated using the Bell basis does not represent the coherence in the system, since there is a coherence in the system due to the choice of the basis states. We first compute the entanglement and quantum coherence in the two qubit mixed states prepared using the Bell states and one of the states from the computational basis. The quantum coherence is estimated using the l1-norm of coherence, the entanglement is measured using the concurrence and the mixedness is measured using the linear entropy. Then we estimate these quantities in the Bell basis and establish that coherence should be measured only in separable basis, whereas entanglement and mixedness can be measured in any basis. We then calculate the teleportation fidelity of these mixed states and find the regions where the states have a fidelity greater than the classical teleportation fidelity. We also examine the violation of the Bell-CHSH inequality to verify the quantum nonlocal correlations in the system. The estimation of the above mentioned quantum correlations, teleportation fidelity and the verification of Bell-CHSH inequality is also done for bipartite states obtained from the tripartite systems by the tracing out of one of their qubits. We find that for some of these states teleportation is possible even when the Bell-CHSH inequality is not violated, signifying that nonlocality is not a necessary condition for quantum teleportation.

quant-ph↗

arXiv2025

Dephasing-Induced Distribution of Entanglement in Tripartite Quantum Systems

Preserving multipartite entanglement amidst decoherence poses a pivotal challenge in quantum information processing. However, assessing multipartite entanglement in mixed states amid decoherence presenting a formidable task. Employing reservoir memory offers a means to attenuate the decoherence dynamics impacting multipartite entanglement, thereby slowing its degradation. One of the important measures which can be implemented to quantify entanglement is the relative entropy of entanglement. Although this measure is not monogamous \cite{horodeckirev2009}, it can universally be applied to both pure and mixed states. Based on this fundamental novelty, in this work, therefore, we introduce a quantifier which will investigate how entanglement remain distributed among the qubits of multipartite states when these states are exposed to multipartite dephasing setting. For our study we use various pure and mixed tripartite states subjected to finite temperature in both Markovian and non-Markovian local/common bath. Here, we consider situations where the three qubits interact with a common reservoir as well as a local bosonic reservoir. We also show that the robustness of a quantum system to decoherence depends on the distribution of entanglement and its interaction with various configurations of the bath. When each qubit has its own local environment, the system exhibits different distribution dynamics compared to when all three qubits share a common environment with one exception regarding a mixed state.

quant-ph↗

arXiv2024

Enhancing the Charging Performance of Many-Body Quantum Batteries through Landau-Zener Driving

We explore the charging advantages of a many-body quantum battery driven by a Landau-Zener field. Such a system may be modeled as a Heisenberg XY spin chain with $\textit{N}$ interacting spin-$\frac{1}{2}$ particles under an external magnetic field. Here we consider both nearest-neighbor and long-range spin interactions. The charging performance of this many-body quantum battery is evaluated by comparing Landau-Zener and periodic driving protocols within these interaction regimes. Our findings show that the Landau-Zener driving can offer superior energy deposition and storage efficiency compared to periodic driving. Notably, the Landau-Zener protocol may deliver optimal performance when combined with long-range interactions. The efficiency of a Landau-Zener quantum battery can be significantly enhanced by optimizing key parameters, such as XY anisotropy, the magnitude of the driving field, and interaction strength.

quant-ph↗

arXiv2024

Inverse Laplace transform based on Widder's method for Tsallis exponential

A generalization of the Laplace transform based on the generalized Tsallis $q$-exponential is given in the present work for a new type of kernel. We also define the inverse transform for this generalized transform based on the complex integration method. We prove identities corresponding to the Laplace transform and inverse transform like the $q$-convolution theorem, the action of generalized derivative and generalized integration on the Laplace transform. We then derive a $q$-generalization of the inverse Laplace transform based on the Post-Widder's method which bypasses the necessity for a complex contour integration. We demonstrate the usefulness of this in computing the Laplace and inverse Laplace transform of some elementary functions. Finally we use the Post-Widder's method based inverse Laplace transform to compute the density of states from the partition function for the case of a generalized classical ideal gas and linear harmonic oscillator in $D$-dimensions.

math-ph↗

arXiv2024

Bell's theorem in time without inequalities

Bell's theorem revealed that a local hidden-variable model cannot completely reproduce the quantum mechanical predictions. Bell's inequality provides an upper bound under the locality and reality assumptions that can be violated by correlated measurement statistics of quantum mechanics. Greenberger, Horne, and Zeilinger (GHZ) gave a more compelling proof of Bell's theorem without inequalities by considering perfect correlations rather than statistical correlations. This work presents a temporal analog of the GHZ argument that establishes Bell's theorem in time without inequalities.

physics.gen-ph↗

arXiv2024

Enhanced quantum synchronization of a driven qubit under non-Markovian dynamics

Synchronizing a few-level quantum system is of fundamental importance to the understanding of synchronization in the deep quantum regime. We investigate quantum phase synchronization of a two-level system (qubit) driven by a semiclassical laser field, in the presence of a general non-Markovian dissipative environment. The phase preference of the qubit is demonstrated through Husimi Q-function, and the existence of a limit cycle is also shown in our system. Synchronization of the qubit is quantified using the shifted phase distribution. The signature of quantum phase synchronization viz the Arnold tongue is obtained from the maximal value of the shifted phase distribution. Two distinct types of qubit dynamics is considered depending on the reservoir correlation time being very short and a situation when bath correlation time is finite. In the Markov regime of the environment, the phase preference of the qubit goes away in the long time limit, whereas the long-time phase localization persists in the non-Markovian regime. We also plot the maximum of the shifted phase distribution in two ways: (a) by varying the detuning and laser driving strength, and (b) by varying the system-bath coupling and laser driving strength. Various system-environment parameters determine the synchronization regions and the qubit phase synchronization is shown to be enhanced in the non-Markov regime.

quant-ph↗

arXiv2023

Entanglement preservation in tripartite quantum systems under dephasing dynamics

Protecting entanglement from decoherence is a critical aspect of quantum information processsing. For many-body quantum systems evolving under decoherence, estimating multipartite entanglement is challenging. This challenge can be met up by considering distance based measure such as relative entropy of entanglement which decisively measures entanglement in both pure as well as mixed states. In this work, we investigate the tripartite entanglement dynamics of pure and mixed states in the presence of a structured dephasing environment at finite temperature. We show that the robustness of the quantum system to decoherence is dependent on the distribution of entanglement and its relation to different configurations of the bath. If the bath is structured individually such that each qubit has its own environment, the system has different dynamics compared to when the bath is common to all the three qubits. From the results we conjecture that there is a connection between the distribution of entanglement among the qubits and the distribution of bath degrees of freedom, and the interplay of these two distributions determines the decay rate of the entanglement dynamics. The sustainability of tripartite entanglement is shown to be enhanced significantly in presence of reservoir memory.

quant-ph↗

arXiv2022

Quantum Uncertainty Dynamics

Quantum uncertainty relations have deep-rooted significance on the formalism of quantum mechanics. Heisenberg's uncertainty relations attracted a renewed interest for its applications in quantum information science. Robertson derived a general form of Heisenberg's uncertainty relations for a pair of arbitrary observables represented by Hermitian operators. In the present work, we discover a temporal version of the Heisenberg-Robertson uncertainty relations for the measurement of two observables at two different times, where the dynamical uncertainties crucially depend on the time evolution of the observables. The uncertainties not only depend on the choice of observables, but they also depend on the times at which the physical observables are measured. The time correlated two-time commutator dictates the trade-off between the dynamical uncertainties. We demonstrate the dynamics of these uncertainty relations for a spin-1/2 system and for a quantum harmonic oscillator. The temporal uncertainty relations discovered in this work can be experimentally verified with the present quantum technology.

quant-ph↗

arXiv2022

Quantum synchronization due to information backflow

The phase synchronization of a single qubit in a dissipative bath in the absence of driving field is demonstrated. Using the Husimi $Q$-function we show that the phase preference is present in the long time limit only during non-Markovian evolution with a finite detuning. This happens due to the information backflow signifying that non-Markovianity is a resource for quantum synchronization. To quantify synchronization we use the shifted phase distribution as well as its maximal value. From the maximal value of the shifted phase distribution we observe the signatures of quantum synchronization {\it viz} the Arnold tongue. In our case the region ofsynchronization is outside the tongue region and the region inside the tongue is the desynchronized region. This is in contrast to the results in the literature, where the synchronization is within the tongue region.

quant-ph↗

arXiv2022

Quantum coherence dynamics of displaced squeezed thermal state in a Non-Markovian environment

The dynamical behavior of quantum coherence of a displaced squeezed thermal state in contact with an external bath is discussed in the present work. We use a Fano-Anderson type of Hamiltonian to model the environment and solve the quantum Langevin equation. From the solution of the quantum Langevin equation we obtain the Green's functions which are used to calculate the expectation value of the quadrature operators which are in turn used to construct the covariance matrix. We use a relative entropy based measure to calculate the quantum coherence of the mode. The single mode squeezed thermal state is studied in the Ohmic, sub-Ohmic and the super-Ohmic limits for different values of the mean photon number. In all these limits, we find that when the coupling between the system and the environment is weak, the coherence decays monotonically and exhibit a Markovian nature. When the system and the environment are strongly coupled, we observe that the evolution is initially Markovian and after some time it becomes non-Markovian. The non-Markovian effect is due to the environmental back action on the system. Finally, we also present the steady state dynamics of the coherence in the long time limit in both low and high temperature regime. We find that the qualitative behavior remains the same in both the low and high temperature limits. But quantitative values differ because the coherence in the system is lower due to thermal decoherence.

quant-ph↗

arXiv2022

Dynamical Crossover from Markovian to Non-Markovian dynamics in the strong coupling regime

The transient dynamics of quantum coherence of Gaussian states are investigated. The state is coupled to an external environment which can be described by a Fano-Anderson type Hamiltonian. Solving the quantum Langevin equation, we obtain the Greens functions which are used to compute the time evolved first and second moments of the quadrature operators. From the quadrature operator moments, we construct the covariance matrix which is used to measure the coherence in the system. The coherence is measured using the relative entropy of coherence measure. We consider three different classes of spectral densities in our analysis viz, the Ohmic, the sub-Ohmic, and the super-Ohmic densities. In our work, we study the dynamics of the coherent state, squeezed state, and displaced squeezed state. For all these states we observe that when the coupling with the system and the environment is weak, the coherence monotonically decreases and eventually vanishes in a long time. Thus all the states exhibit Markovian evolution in the weak coupling limit. In the strong coupling limit, the dynamics for the initial period is Markovian and after a certain period, it becomes non-Markovian where we observe an environmental backaction on the system. Thus in the strong coupling limit, we observe a dynamical crossover from Markovian nature to non-Markovian behavior. This crossover is very abrupt under some environmental conditions and for some parameters of the quantum state. Using a quantum master equation approach we verify the crossover from the dynamics of the dissipation and fluctuation parameters and the results endorse those obtained from coherence dynamics.

quant-ph↗

arXiv2020

Fragility of quantum correlations and coherence in a multipartite photonic system

Certain quantum states are well-known to be particularly fragile in the presence of decoherence, as illustrated by Schrodinger's famous gedanken cat experiment. It has been better appreciated more recently that quantum states can be characterized in a hierarchy of quantum quantities such entanglement, quantum correlations, and quantum coherence. It has been conjectured that each of these quantities have various degrees of fragility in the presence of decoherence. Here we experimentally confirm this conjecture by preparing tripartite photonic states and subjecting them to controlled amounts of dephasing. When the dephasing is applied to all the qubits, we find that the entanglement is the most fragile quantity, followed by the quantum coherence, then mutual information. This is in agreement with the widely held expectation that multipartite quantum correlations are a highly fragile manifestation of quantumness. We also perform dephasing on one out of the three qubits on star and $ W \bar{W} $ states. Here the distribution of the correlations and coherence in the state becomes more important in relation to the dephasing location.

quant-ph↗

arXiv2018

Quantum thermodynamics of single particle systems

Classical thermodynamics is built with the concept of equilibrium states. However, it is less clear how equilibrium thermodynamics emerges through the dynamics that follows the principle of quantum mechanics. In this paper, we develop a theory to study the exact nonequilibrium thermodynamics of quantum systems that is applicable to arbitrary small systems, even for single particle systems, in contact with a reservoir. We generalize the concept of temperature into nonequilibrium regime that depends on the detailed dynamics of quantum states. When we apply the theory to the cavity system and the two-level atomic system interacting with a heat reservoir, the exact nonequilibrium theory unravels unambiguously (1) the emergence of classical thermodynamics from quantum dynamics in the weak system-reservoir coupling regime, without introducing equilibrium hypothesis; (2) the breakdown of classical thermodynamics in the strong coupling regime, which is induced by non-Markovian memory dynamics; and (3) the occurrence of dynamical quantum phase transition characterized by inflationary dynamics associated with a negative nonequilibrium temperature, from which the third law of thermodynamics, allocated in the deep quantum realm, is naturally proved. The corresponding dynamical criticality provides the border separating the classical and quantum thermodynamics. The inflationary dynamics may also provide a simple picture for the origin of big bang and universe inflation.

quant-ph↗

arXiv2018

Operational criterion for controlled dense coding with non-trivial tripartite entangled states

In this paper, we provide an operational criterion for controlled dense coding with a general class of three-qubit partially entangled states. A general three-qubit pure entangled state can be classified into two inequivalent classes according to their genuine tripartite entanglement. We claim that if a three-qubit state shows entanglement characteristic similar to $GHZ$-class then such non-trivial tripartite states are useful in {\it controlled dense coding} whereas states belonging to $W$-class are not useful for that. We start with a particular class of non-trivial partially entangled states belonging to $GHZ$-class and show that they are effective in controlled dense coding. Then we cite several other examples of different types of tripartite entangled states to support our conjecture.

quant-ph↗

arXiv2017

Time dynamics of quantum coherence and monogamy in a non-Markovian environment

The time evolution of the distribution and shareability of quantum coherence of a tripartite system in a non-Markovian environment is examined. The total coherence can be decomposed into various contributions, ranging from local, global bipartite and global tripartite, which characterize the type of state. We identify coherence revivals for non-Markovian systems for all the contributions of coherence. The local coherence is found to be much more robust under the environmental coupling due to an effective smaller coupling to the reservoir. This allows us to devise a characterization of a quantum state in terms of a coherence tuple on a multipartite state simply by examining various combinations of reservoir couplings. The effect of the environment on the shareability of quantum coherence, as defined using the monogamy of coherence, is investigated and found that the sign of the monogamy is a preserved quantity under the decoherence. We conjecture that the monogamy of coherence is a conserved property under local incoherent processes.

quant-ph↗

arXiv2017

Probing nonclassicality under spontaneous decay

We investigate the nonclassicality of an open quantum system using Leggett-Garg inequality (LGI) which test the correlations of a single system measured at different times. Violation of LGI implies nonclassical behavior of the open system. We investigate the violation of the Leggett-Garg inequality for a two level system (qubit) spontaneously decaying under a general non-Markovian dissipative environment. Our results are exact as we have calculated the two-time correlation functions exactly for a wide range of system-environment parameters beyond Born-Markov regime.

quant-ph↗