Searcharxiv⌕ Search

arXiv subjects

B. Mojaveri

Publications and source records attributed to B. Mojaveri.

15 recordsLinked to original sources
arXiv2024

Adiabatic charging of open quantum battery

We revisit the adiabatic charging of a three-level QBs, using the adiabatic quantum master equation formalism. We restrict ourselves to the weak-coupling regime with an Ohmic thermal bath and investigate the effects of relaxation and dephasing on the charging process. We analyze the dependence of the stored energy, ergotropy as well as efficiency of QB on the total time of evolution $t_f$. We demonstrate that for very short charging time ($t_f$), where the evolution is highly non-adiabatic, the stored energy and ergotropy are very small. However, with increasing $t_f$ we show that there is an optimal charging time, $t_f^{opt}$, for maximum energy charging such that at low temperatures we could fully charge the battery and effectively extract the whole amount of energy from it. Note that, the optimal charging time could be decreased by adjusting strength of the coupling between system and environment and also appropriate choice of the Hamiltonian parameters which in turn speed up the charging process. On the other hand, we show that for very long charing time $t_f$ the charging energy, ergotropy and efficiency decrease due to thermal excitations. Furthermore to get more insights about the problem we investigate the distance between density matrix of system at optimal charging time $t_f^{opt}$ and the corresponding thermal state using one-norm distance.

quant-ph↗
arXiv2023

Enhancing the performance of an open quantum battery by adjusting its velocity

The performance of open quantum batteries (QBs) is severely limited by decoherence due to the interaction with the surrounding environment. So, protecting the charging processes against decoherence is of great importance for realizing QBs. In this work we address this issue by developing a charging process of a qubit-based open QB composed of a qubit-battery and a qubit-charger, where each qubit moves inside an independent cavity reservoir. Our results show that, in both the Markovian and non-Markovian dynamics, the charging characteristics, including the charging energy, efficiency and ergotropy, regularly increase with increasing the speed of charger and battery qubits. Interestingly, when the charger and battery move with higher velocities, the initial energy of the charger is completely transferred to the battery in the Markovian dynamics. In this situation, it is possible to extract the total stored energy as work for a long time. Our findings show that open moving-qubit systems are robust and reliable QBs, thus making them a promising candidate for experimental implementations.

quant-ph↗
arXiv2016

Cat-States in the Framework of Wigner-Heisenberg Algebra

A one-parameter generalized Wigner-Heisenberg algebra( WHA) is reviewed in detail. It is shown that WHA verifies the deformed commutation rule $[\hat{x}, \hat{p}_λ] = i(1 + 2λ\hat{R})$ and also highlights the dynamical symmetries of the pseudo-harmonic oscillator( PHO). \textbf{The present article is devoted to the study of new cat-states} built from $λ$-deformed Schrödinger coherent states, which according to the Barut-Girardello scheme are defined as the eigenstates of the generalized annihilation operator. Particular attention is devoted to the limiting case where the Schrödinger cat states are obtained. Nonclassical features and quantum statistical properties of these states are studied by evaluation of Mandel's parameter and quadrature squeezing with respect to the $λ-$deformed canonical pairs $( \hat{x}, \hat{p}_λ)$. It is shown that these states minimize the uncertainty relations of each pair of the $su(1,1)$ components.

quant-ph↗
arXiv2016

Approach to a Parity Deformed Jaynes-Cummings Model and the Maximally Entangled States

A parity deformed Jaynes-Cummings model (JCM) is introduced, which describes an interaction of a two-level atom with a $λ$-deformed quantized field. In the rotating wave approximation (RWA), all eigen-values and eigen-functions of this model are obtained exactly. Assuming that initially the field is prepared in the Wigner cat state (WCS) and the two-level atom is in the excited state, it has been shown that the atomic Rabi oscillations exhibit a quasi-periodic behavior in the collapse and revival patterns. The influence of the deformation parameter on the time evolution of non-classical features of the radiation field such as the sub-Poissonian statistics and squeezing effect are also analyzed. Interestingly, the main finding here is that we can realize maximally entangled atom-field states. In this note it is shown that the high fidelity is possible in the weak coupling regime, while the deformation parameter becomes large values.

quant-ph↗
arXiv2014

Approach of the Generating Functions to the Coherent States for Some Quantum Solvable Models

We introduce to this paper new kinds of coherent states for some quantum solvable models: a free particle on a sphere, one-dimensional Calogero-Sutherland model, the motion of spinless electrons subjected to a perpendicular magnetic field B, respectively, in two dimensional flat surface and an infinite flat band. We explain how these states come directly from the generating functions of the certain families of classical orthogonal polynomials without the complexity of the algebraic approaches. We have shown that some examples become consistent with the Klauder- Perelomove and the Barut-Girardello coherent states. It can be extended to the non-classical, q-orthogonal and the exceptional orthogonal polynomials, too. Especially for physical systems that they don't have a specific algebraic structure or involved with the shape invariance symmetries, too.

math-ph↗
arXiv2014

Excited Coherent States Attached to Landau Levels

A new scheme is proposed to design excited coherent states. where the states $β$,$α$ denote the Glauber two variable minimum uncertainty coherent states, which minimize minimum uncertainty conditions while carrier nonclassical properties too and n is an integer. They are converted into the Agarwal's type of the photon added coherent states, arbitrary Fock states and the Glauber two variable coherent states, respectively depending on which of the parameters $\b{eta}$,$α$ and $n$ equal to zero. It has been shown that the resolution of identity condition is realized with respect to an appropriate measure on the complex plane, too. We have compared our results with the similar quantum states of Agarwal's type and seen that in our case amount of quantum fluctuations are much controllable. Moreover, we have also more flexibility to establish and set-out of their features. Also, there is a discussion on the statistical properties, can unveil (non-)classical properties of these states. For instance their Poissonian statistics are significant similar to what we saw earlier in the Glauber two variable coherent states. Interestingly, depending on the particular choice of the parameters of the above scenarios, we are able to determine the status of compliance with squeezing properties in field quadratures. The last stage is devoted to some theoretical framework to generate them in cavities.

math-ph↗
arXiv2014

Generalized Coherent States for the Spherical Harmonics $Y_{m}^{m}(θ,ϕ)$

The associated Legendre functions $P_{l}^{(m)}(x)$ for a given $l-m$, may be taken into account as the increasing infinite sequences with respect to both indices $l$ and $m$. This allows us to construct the exponential generating functions for them in two different methods by using Rodrigues formula. As an application then we present a scheme to construct generalized coherent states corresponding to the spherical harmonics $Y_{m}^{m}(θ,ϕ)$.

math-ph↗
arXiv2014

Landau Levels as a Limiting Case of a Model with the Morse-Like Magnetic Field

We consider the quantum mechanics of an electron trapped on an infinite band along the $x$-axis in the presence of the Morse-like perpendicular magnetic field $\vec{B}=-B_{0}e^{-\frac{2π}{a_{0}}x}\hat{k}$ with $B_{0}>0$ as a constant strength and $a_{0}$ as the width of the band. It is shown that the square integrable pure states realize representations of $su(1,1)$ algebra via the quantum number corresponding to the linear momentum in the $y$-direction. The energy of the states increases by decreasing the width $a_{0}$ while it is not changed by $B_{0}$. It is quadratic in terms of two quantum numbers, and the linear spectrum of the Landau levels is obtained as a limiting case of $a_{0}\rightarrow\infty$. All of the lowest states of the $su(1,1)$ representations minimize uncertainty relation and the minimizing of their second and third states is transformed to that of the Landau levels in the limit $a_{0}\rightarrow\infty$. The compact forms of the Barut-Girardello coherent states corresponding to $l$-representation of $su(1,1)$ algebra and their positive definite measures on the complex plane are also calculated.

quant-ph↗
arXiv2014

Generalized $su(2)$ coherent states for the Landau levels and their nonclassical properties

Following the lines of the recent papers [J. Phys. A: Math. Theor. 44, 495201 (2012); Eur. Phys. J. D 67, 179 (2013)], we construct here a new class of generalized coherent states related to the Landau levels, which can be used as the finite Fock subspaces for the representation of the $su(2)$ Lie algebra. We establish the relationship between them and the deformed truncated coherent states. We have, also, shown that they satisfy the resolution of the identity property through a positive definite measures on the complex plane. Their nonclassical and quantum statistical properties such as quadrature squeezing, higher order `$su(2)$' squeezing, anti-bunching and anti-correlation effects are studied in details. Particularly, the influence of the generalization on the nonclassical properties of two modes is clarified.

quant-ph↗
arXiv2014

Generalized $su(1,1)$ coherent states for pseudo harmonic oscillator and their nonclassical properties

In this paper we define a non-unitary displacement operator, which by acting on the vacuum state of the pseudo harmonic oscillator (PHO), generates new class of generalized coherent states (GCSs). An interesting feature of this approach is that, contrary to the Klauder-Perelomov and Barut-Girardello approaches, it does not require the existence of dynamical symmetries associated with the system under consideration. These states admit a resolution of the identity through positive definite measures on the complex plane. We have shown that the realization of these states for different values of the deformation parameters leads to the well-known Klauder-Perelomov and Barut-Girardello CSs associated with the $su(1,1)$ Lie algebra. This is why we call them the generalized $su(1,1)$ CSs for the PHO. Finally, study of some statistical characters such as squeezing, anti-bunching effect and sub-Poissonian statistics reveals that the constructed GCSs have indeed nonclassical features.

math-ph↗
arXiv2012

SU(1,1) Nonlinear Coherent States

The idea of construction of the nonlinear coherent states based on the hypergeometric- type operators associated to the Weyl-Heisenberg group [J:P hys:A 45(2012) 095304], are generalized to the similar states for the arbitrary Lie group SU(1, 1). By using of a discrete, unitary and irreducible representation of the Lie algebra su(1, 1) wide range of generalized nonlinear coherent states(GNCS) have been introduced, which admit a resolution of the identity through positive definite measures on the complex plane. We have shown that realization of these states for different values of the deformation pa- rameters r = 1 and 2 lead to the well-known Klauder-Perelomov and Barut-Girardello coherent states associated to the Irreps of the Lie algebra su(1, 1), respectively. It is worth to mention that, like the canonical coherent states, GNCS possess the temporal stability property. Finally, studying some statistical characters implies that they have indeed nonclassical features such as squeezing, anti-bunching effect and sub-Poissonian statistics, too.

math-ph↗
arXiv2012

Exponential generating functions for the associated Bessel functions

Similar to the associated Legendre functions, the differential equation for the associated Bessel functions $B_{l,m}(x)$ is introduced so that its form remains invariant under the transformation $l\rightarrow -l-1$. A Rodrigues formula for the associated Bessel functions as squared integrable solutions in both regions $l<0$ and $l\geq 0$ is presented. The functions with the same $m$ but with different positive and negative values of $l$ are not independent of each other, while the functions with the same $l+m$ ($l-m$) but with different values of $l$ and $m$ are independent of each other. So, all the functions $B_{l,m}(x)$ may be taken into account as the union of the increasing (decreasing) infinite sequences with respect to $l$. It is shown that two new different types of exponential generating functions are attributed to the associated Bessel functions corresponding to these rearranged sequences.

math-ph↗
arXiv2012

4+1 dimensional homogeneous anisotropic string cosmological models

We present exact solutions of string cosmological models characterized by five dimensional metrics (with four-dimensional real Lie groups as isometry groups), space independent dilaton and vanishing torsion. As an example we consider VII 0 \oplus R model and show that it is equivalent to the (4 +1)-dimensional cosmological model coupled to perfect fluid with negative deceleration parameters (accelerating universe).

hep-th↗
arXiv2008

A fresh look at neutral meson mixing

In this work we show that the existence of a complete biorthonormal set of eigenvectors of the effective Hamiltonian governing the time evolution of neutral meson system is a necessary condition for diagonalizability of such a Hamiltonian. We also study the possibility of probing the $CPT$ invariance by observing the time dependence of cascade decays of type $P^{\circ}(\bar{P^{\circ}})\to \{M_a,M_b\}X\to fX$ by employing such basis and exactly determine the $CPT$ violation parameter by comparing the time dependence of the cascade decays of tagged $P^{\circ}$ and tagged $\bar{P^{\circ}}$.

hep-ph↗