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Fardin Kheirandish

Publications and source records attributed to Fardin Kheirandish.

At least 19 recordsLinked to original sources
arXiv2026

Quantum Dynamics of Interacting oscillators in a thermal medium: A novel scheme

We develop an exact analytical framework for studying the nonequilibrium dynamics of interacting quantum harmonic oscillators coupled to a modelled thermal reservoir and driven by external classical fields. The total Hamiltonian is diagonalized via successive Bogoliubov transformations, enabling a nonperturbative treatment of dissipation and driving. For two coupled oscillators with an external source applied to the first, we derive explicit energy expressions and analyze their dependence on coupling and bath parameters. The phase-space structure is characterized through Husimi $Q$-functions for initial separable coherent and number states. We obtain the reduced density matrix elements in the number-state basis and demonstrate that, in the absence of driving and at zero temperature, the reduced density matrix of the main system satisfies the Lindblad master equation. A generating function for the Husimi function is introduced to facilitate computation of higher-order correlations. The analysis is then generalized to $n$ interacting oscillators, with analytical energy expressions provided and the case $n=3$ examined in detail. Our results establish a versatile and exact framework for driven-dissipative quantum systems, with potential applications in quantum thermodynamics, open quantum systems, and many-body physics.

quant-ph↗
arXiv2026

Markovian evolution from a novel scheme

The Markovian dynamics of open quantum many-body systems are typically governed by the Lindblad master equation, yet obtaining the reduced density matrix for bosonic and fermionic systems remains a formidable numerical challenge due to the exponential growth of the Hilbert space. Here, we introduce a computationally efficient framework for constructing the reduced density matrix by modeling the environment as a copy of the primary system with a monotonically decaying coupling that enforces unidirectional energy flow. Our method directly yields exact solutions that rigorously satisfy the Lindblad master equation for both bosonic and fermionic cases, bypassing the need for costly Liouvillian diagonalization. We validate our approach through applications to paradigmatic models, demonstrating accurate reproduction of dissipative dynamics across a broad parameter regime. This work provides a straightforward and powerful tool for simulating Markovian open-system evolution, with immediate applicability to quantum transport and control problems in many-body physics.

quant-ph↗
arXiv2025

The Mpemba effect in quantum oscillating and two-level systems

The Empemba effect (ME) is investigated in the context of ubiquitous quantum oscillating and two-level systems (TLS) using a novel approach (DOI 10.1088/1402-4896/ad97f1). Exact reduced density matrices for various initial states are derived. The temporal behavior of the trace distance for these initial states is calculated analytically and presented. For a dissipative quantum oscillating system, it is demonstrated that number states $|N\rangle$ intersect with coherent states $|α\rangle$, with this intersection occurring earlier for smaller values of $N$. Additionally, thermal states intersect with coherent states for specific values of $|α|$, leading to the occurrence of the ME in these two scenarios. A weaker version of the ME is also observed for thermal and number states. In the case of a quantum TLS, it is shown that the ME effect occurs, and the potential for its realization and experimental observation is discussed, with reference to the Jaynes-Cummings model (JCM) involving a decaying time-dependent coupling function.

quant-ph↗
arXiv2025

Quantum dynamics of a bosonic mode and a two-level system interacting with several reservoirs

In the framework of a novel dissipative scheme, we have investigated the quantum dynamics of an oscillating system interacting with two reservoirs with different temperatures trough different time-dependent coupling functions. The reduced density matrix, quantum optical characteristic functions, and (quasi) distribution functions like Husimi, Glauber-Sudarshan and Wigner functions on the phase space of the oscillator are obtained. The problem has been generalized to the case where the oscillator is interacting with $n$ distinctive reservoirs, and a quantum current and an effective reservoir is introduced. Finally, the quantum dynamics of a two-level system interacting with two reservoirs has been investigated, and the exact reduced density matrix is obtained.

quant-ph↗
arXiv2025

Faster calculations of optical trapping using neural networks trained by T-matrix data: an application to micro and nanoplastics

We employ neural networks to improve and speed up optical force calculations for dielectric particles. The network is first trained on a limited set of data obtained through accurate light scattering calculations, based on the Transition matrix method, and then used to explore a wider range of particle dimensions, refractive indices, and excitation wavelengths. This computational approach is very general and flexible. Here, we focus on its application in the context of micro and nanoplastics, a topic of growing interest in the last decade due to their widespread presence in the environment and potential impact on human health and the ecosystem.

physics.optics↗
arXiv2024

A novel scheme for modelling dissipation or thermalization in open quantum systems

In this letter, we introduce a novel method for investigating dissipation (gain) and thermalization in an open quantum system. In this method, the quantum system is coupled linearly with a copy of itself or with another system described by a finite number of bosonic operators. The time-dependent coupling functions play a fundamental role in this scheme. To demonstrate the efficiency and significance of the method, we apply it to some ubiquitous open quantum systems. Firstly, we investigate a quantum oscillator in the presence of a thermal bath at the inverse temperature $β$, obtaining the reduced density matrix, the Husimi distribution function, and the quantum heat distribution function accurately. The results are consistent with existing literature by appropriate choices for the time-dependent coupling function. To illustrate the generalizability of this method to systems interacting with multiple thermal baths, we study the interaction of a quantum oscillator with two thermal baths at different temperatures and obtain compatible results. Subsequently, we analyze a two-level atom with energy or phase dissipation and derive the spontaneous emission and the pure dephasing processes consistently using the new method. Finally, we investigate the Markovianity in a dissipative two-level system.

quant-ph↗
arXiv2024

Dynamics of a V-type atom inside a deformed cavity field and in the presence of an external Microwave field

In this article, we explore the interaction between a V-type atom inside a single mode deformed cavity field in the presence of an external microwave field. The Hamiltonian describing the system is derived from the standard Jaynes-Cummings model by deforming the field operators based on the Kerr-induced interaction. The total and reduced density matrices are obtained and the temporal evolution of nonclassical properties such as the Mandel Q parameter, quantum entanglement, and the position-momentum uncertainty relation (squeezing) of the field are examined. The impacts of coupling constant, generalized Kerr medium, and the intensity-dependent coupling function on the nonclassical indicators are thoroughly analyzed.

quant-ph↗
arXiv2023

Exploring new subclass of k-inflation: tachyon inflation in $R+ηT$ gravity model

It is explained that any scalar field in $f(R,T)$ gravity model could present a new subclass of the k-essence model for inflation. While the case of the quintessence has been studied, there is an empty gap required to be filled by investigating more types of field models. Here, we are aiming to partially fill the gap and concentrate on the tachyon field. In this study, we explore the phenomenon of tachyon inflation in the context of the alternative gravity theory $f(R,T) = R + ηT$. By applying slow-roll approximations, we examine the model in detail for three different potentials: power-law, generalized T-mode, and inverse hyperbolic cosh. Using observational data and Python coding, we determine a range of values for the model's free parameters that allow it to fit the data perfectly. In essence, this study provides a comprehensive analysis of tachyon inflation in the $R + ηT$ gravity theory, offering new insights into this alternative framework and its potential to explain tachyon inflation.

gr-qc↗
arXiv2023

Structured matter wave evolution in external time-dependent fields

In the present work, we have analyzed the motion of a structured matter wave in the presence of a constant magnetic field and under the influence of a time-dependent external force. We have introduced exact propagator kernels obtained from partial differential equations based on the Heisenberg equations of motion. The initial wave function is assumed as a Gauss-Hermite wave function. For the evolved wave function, we have obtained and discussed the uncertainties, orbital angular momentum, and the inertia tensor in the center of mass frame of the density function. From the point of view of the quantum interferometry of matter waves, and also non-relativistic quantum electron microscopy, the results obtained here are important and more reliable than the approximate methods like the axial approximation.

quant-ph↗
arXiv2023

Quantum propagator for a general time-dependent quadratic Hamiltonian: Application to interacting oscillators in external fields

In this paper, we find the quantum propagator for a general time-dependent quadratic Hamiltonian. The method is based on the properties of the propagator and the fact that the quantum propagator fulfills two independent partial differential equations originating from Heisenberg equations for positions and momenta. As an application of the method, we find the quantum propagator for a linear chain of interacting oscillators for both periodic and Dirichlet boundary conditions. The state and excitation propagation along the harmonic chain in the absence and presence of an external classical source is studied and discussed. The location of the first maxima of the probability amplitude $P(n,τ)$ is a straight line in the $(n,τ)$-plane, indicating a constant speed of excitation propagation along the chain.

quant-ph↗
arXiv2022

On quantum states generated from interacting oscillators

In this paper, we study the quantum states generated from two and three linearly interacting quantum harmonic oscillators. We consider the possibility that one of the oscillators be under the influence of a classical external source and obtain the total and reduced density matrices related to the system. We show how the problem can be generalized to n linearly interacting oscillators straightforwardly.

quant-ph↗
arXiv2020

Many-body work distributions

The work distribution function for a non-relativistic, non-interacting quantum many-body system interacting with classical external sources is investigated. Exact expressions for the characteristic function corresponding to the work distribution function is obtained for arbitrary switching function and coupling functions. The many-body frequencies are assumed to be generally time-dependent in order to take into account the possibility of moving the boundaries of the system in a predefined process linking the characteristic function to the fluctuation-induced energies in confined geometries. Some limiting cases are considered and discussed.

quant-ph↗
arXiv2019

Open quantum systems in Heisenberg picture

In the framework of the Heisenberg picture, an alternative derivation of the reduced density matrix of a driven dissipative quantum harmonic oscillator as the prototype of an open quantum system is investigated. The reduced density matrix for different initial states of the combined system is obtained from a general formula, and different limiting cases are studied. Exact expressions for the corresponding characteristic function in quantum thermodynamics and Wigner quasi distribution function are found. A possible generalization based on the Magnus expansion of the evolution operator is presented.

quant-ph↗
arXiv2018

Exact Density matrix of an oscillator-bath system: Alternative derivation

Starting from a total Lagrangian describing an oscillator-bath system, a novel derivation of exact quantum propagator is presented. Having the quantum propagator, the exact density matrix, reduced density matrix of the main oscillator and thermal equilibrium fixed point are obtained. The problem is generalised to the cases where the main oscillator is under the influence of a classical external force. By introducing generalised auxiliary classical fields, the generalised quantum propagator or generating functional of position correlation functions is obtained.

quant-ph↗
arXiv2018

A novel derivation of quantum propagator useful for time-dependent trapping and control

A novel derivation of quantum propagator of a system described by a general quadratic Lagrangian is presented in the framework of Heisenberg equations of motion. The general corresponding density matrix is obtained for a derived quantum harmonic oscillator and a particle confined in a one dimensional Paul trap. Total mean energy, work and absorbed heat, Wigner function and excitation probabilities are found explicitly. The method presented here is based on the Heisenberg representation of position and momentum operators and can be generalized to a system consisting of a set of linearly interacting harmonic oscillators straightforwardly.

quant-ph↗
arXiv2018

From Brownian motion formalism to fluctuation-induced force in a general fluctuating medium

Starting from a microscopic approach and using the formalism of quantum Brownian motion, partition function of a system composed of two separated pieces of anisotropic matter and a fluctuating medium in finite temperature is obtained rigorously. A general expression for fluctuation-induced free energy between the separated anisotropic pieces of matter is obtained and it is shown that in the framework of induced-force, the free energy of mean-force and effective free energy are equivalent.

quant-ph↗
arXiv2017

Hamiltonian of mean force and a damped harmonic oscillator in an anisotropic medium

The quantum dynamics of a damped harmonic oscillator is investigated in the presence of an anisotropic heat bath. The medium is modeled by a continuum of three dimensional harmonic oscillators and anisotropic coupling is treated by introducing tensor coupling functions. Starting from a classical Lagrangian, the total system is quantized in the framework of the canonical quantization. Following Fano technique, Hamiltonian of the system is diagonalized in terms of creation and annihilation operators that are linear combinations of the basic dynamical variables. Using the diagonalized Hamiltonian, the mean force internal energy, free energy and entropy of the damped oscillator are calculated.

quant-ph↗