arXiv subjects

Dušan Popov

Publications and source records attributed to Dušan Popov.

11 recordsLinked to original sources

arXiv2026

Some properties of coherent states with singular complex matrix argument

In the paper our aim was to study the properties of a new version of coherent states whose argument is a linear combination of two special singular square 2 x 2 matrix, having a single nonzero element, equal to 1, and two labeling complex variables as developing coefficients. We have shown that this new version of coherent states satisfies all the conditions imposed on coherent states, both of pure, as well as the mixed (thermal) states characterized by the density operator. As applications, we examined the connection between these coherent states and the notions of qubits and von Neuman entropy.

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arXiv2025

Generalized coherent states in thermal field dynamics in the frame of diagonal ordering operator technique

Although the thermofield dynamics (TFD) was developed specifically for systems to which the ladder canonical operators and are associated, in the paper we showed that this approach can also be formulated for systems of deformed bosons, associated with a pair of deformed operators and . In this context we built sets of temperature dependent coherent states, both of the Barut-Girardello and of the Klauder-Perelomov type, these two types being dual to each other. In calculations involving ladder operators, both independent and temperature-dependent, we used the Diagonal Operator Ordering Technique (DOOT), which is a generalization of the Integration Within an Ordered Product technique (IWOP) applicable to canonical operators associated with the one-dimensional harmonic oscillator. We also refer to the connection between TFD and thermodynamic quantities.

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arXiv2025

Generalized coherent states with shifted (displaced) arguments

In the paper we developed a procedure for constructing generalized coherent states with shifted argument, as a result of the action of the generalized displacement operator. This was based on the action of a pair of nonlinear ladder operators, which generate nonlinear coherent states. To examine the properties of coherent states with shifted argument, the rules of the normal operator ordering technique (DOOT) were used. The results obtained were verified for a series of particular cases, obtaining expressions consistent with those in the literature. The expressions obtained will be, among others, useful in quantum optics, e.g. for calculating the Wigner operator in the representation of coherent states.

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arXiv2024

Four-parameter Mittag-Leffler functions and their associated coherent states

We defined and used a pair of Hermitian annihilation and creation operators which generate the generalized coherent states, defined in the Barut-Girardello manner, whose normalization function is just the four-parameter generalized Mittag-Leffler function. We examined the characteristic properties for these pure, as well as mixed (thermal) coherent states. All calculations are made using the rules of the technique of diagonal ordering of operators. Finally, the integral counterpart of the Mittag-Leffler coherent states are examined which is connected with nu-function. The paper is an example of the application of a mathematical entity (Mittag-Leffler function) in quantum mechanics (coherent states formalism).

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arXiv2024

Some new considerations about the $ν$-function

The present paper starts from a previously deduced result, in which the $ν$-function plays the role of the normalization function of generalized hypergeometric coherent states for quantum systems with a continuous spectrum. We have generalized this idea, obtaining a new function, the generalized $ν$-function. By defining a discrete-continuous limit, we revealed a series of interesting properties that, in the last instance, allow the formulation and solution of new integrals involving the generalized $ν$-functions which depend on both scalar arguments as well as those containing creation and annihilation operators, which generate the generalized hypergeometric coherent states. To our knowledge, the results obtained by us do not appear in the literature.

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arXiv2024

Connection between coherent states and some integrals and integral representations

The paper presents an interesting mathematical feedback between the formalism of coherent states and the field of integrals and integral representations involving special functions. This materializes through an easy and fast method to calculate integrals or integral representations of different functions, expressible by means of Meijer's G-, as well as hypergeometric generalized functions. The feedback starts from a fundamental integral that comes from the decomposition of the unity operator in the language of coherent states from quantum mechanics. In this way, integrals and integral representations are obtained, some that do not appear in the literature, and others already known, which can be verified by orthodox methods. All calculations are made using the properties of the diagonal operators ordering technique (DOOT), a relatively new technique of normal ordering of the creation and annihilation operators in quantum mechanics. The paper contributes to increasing the number of solvable integrals involving special functions.

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arXiv2024

An application of the theta operator in generalized hypergeometric coherent states formalism

In this paper we examine one of the multiple applications of the theta operator xd/dx in quantum mechanics, namely, in the formalism of generalized hypergeometric coherent states (GHG CSs). These states are the most general coherent states, in the sense that from them, through particularization, all coherent states with physical meaning can be obtained. A series of new results were obtained and some already known ones were found / confirmed (the integral representations, as well as the Laplace transform of hypergeometric functions). To support the theoretical considerations presented above, we examined, as example, the quantum systems with a linear energy spectrum. The results obtained in this paper contribute to widening the area of applicability of the theta operator.

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arXiv2024

About some properties of the canonical density matrix versus the canonical Bloch equation

We examine some properties of the non-normalized (or canonical) density matrix in the coherent states representation, by two equivalent ways. On the one hand by its definition, and on the other hand as a solution to Bloch's canonical equation. It is concluded that, since in many cases Bloch's differential equation is difficult to solve, in applications it is preferable to use the expression obtained directly from the definition of the canonical density matrix in the coherent states representation. This conclusion is verified by examining several cases of quantum systems with linear or quadratic energy spectrum.

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arXiv2023

Free particle trapped in an infinite quantum well examined through the discrete calculus model

We use the discrete approach to solve the Schrödinger as well as the Bloch equations for a free particle and the quantum gas of free particles embedded in an infinite quantum well with the finite width. We obtain the expressions of energy eigenvalues, the eigenfunctions as well as the density matrix and partition function for the discrete case. By applying the continuous quantum mechanics limit we recover the corresponding results in the continuous-variable quantum mechanics.

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arXiv2023

Considerations of the duality in generalized coherent states formalism

In the paper, a pair of dual operators is introduced with which a dual pair of generalized displacement operators is constructed. With these entities it is shown that the Barut - Girardello and Klauder - Perelomov generalized coherent states are dual states. The characteristics of these coherent states are constructed, separately and comparatively.

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arXiv2022

A generalized Fourier transform of the P-quasi distribution function

In the paper we made a generalization of the Fourier transform in the complex space, applicable to the pair of Husimi and P-quasi distributions, in the representation of nonlinear coherent states. Implicitly, our result is a generalization similar result of Mehta, but which referred only to the canonical coherent states (associated with the one-dimensional harmonic oscillator). Our result is valid for both types of coherent states (defined in the Barut-Girardello, respectively Klauder-Perelomov manner).

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