Oksana A. Koval

Bio: Oksana A. Koval is an academic researcher from Russian Academy of Sciences. The author has contributed to research in topics: Phase (waves) & Dipole. The author has an hindex of 2, co-authored 5 publications receiving 6 citations.

Aspects of arbitrarily oriented dipoles scattering in a plane: Short-range interaction influence

Abstract: The impact of the short-range interaction on the resonances' occurrence in the anisotropic dipolar scattering in a plane is numerically investigated for the arbitrarily oriented dipoles and for a wide range of collision energies. We reveal the strong dependence of the cross section of the two-dimensional (2D) dipolar scattering on the radius of short-range interaction, which is modeled by a hard wall potential and by the more realistic Lennard-Jones potential, and on the mutual orientations of the dipoles. We define the critical (magic) tilt angle of one of the dipoles, depending on the direction of the second dipole for arbitrarily oriented dipoles. We find that resonances arise only when this angle is exceeded. In contrast to the three-dimensional (3D) case, the energy dependencies of the boson (fermion) 2D scattering cross section grow (are reduced) with an energy decrease in the absence of the resonances. We show that the mutual orientation of dipoles strongly impacts the form of the energy dependencies, which begin to oscillate with the tilt angle increase, unlike the 3D dipolar scattering. The angular distributions of the differential cross section in the 2D dipolar scattering of both bosons and fermions are highly anisotropic at nonresonant points. The results of the accurate numerical calculations of the cross section agree well with the results obtained within the Born and eikonal approximations.

Numerical analysis of energy levels of quantum particle in field of two-dimensional dipole

Abstract: Аннотация. Целью работы является численное исследование энергетических уровней связанных состояний квантовой частицы в поле двумерного диполя с помощью предложенного численного алгоритма для решения двумерного уравнения Шредингера. Процедура и методы. С помощью специального разложения волновой функции двумерное уравнение Шредингера сведено к решению краевой задачи Штурма-Лиувилля для системы дифференциальных уравнений. Для решения задачи поиска собственных значений матрицы, получаемой при конечно-разностной аппроксимации производных, применён метод обратных итераций со сдвигом. Результаты. Определены значения уровней энергии и соответствующие им собственные волновые функции квантовой частицы в поле двумерного диполя. Теоретическая и/или практическая значимость. С помощью предложенного численного алгоритма с хорошей точностью получены значения энергетических уровней связанных состояний квантовой частицы в поле двумерного диполя. Получено согласие с результатами других авторов, использовавших вариационный подход, для которого отсутствуют оценки ошибок вычисленных значений относительно истинного решения. Выполненные нами расчёты с известной оценкой точности восполняют этот пробел. Ключевые слова: двумерное уравнение Шредингера, анизотропные взаимодействия, численный алгоритм Благодарности. Работа выполнена при финансовой поддержке Российского фонда фундаментальных исследований (грант No 19-32-80003).

Method of Spherical Phase Screens for Modeling the Propagation of Diverging Beams in Inhomogeneous Media

Abstract: The phase-screen (split-step) method is widely used for modeling wave propagation in inhomogeneous media. The method of plane phase screens is best known. However, for modeling a 2D problem of radio occultation sounding of the Earth’s atmosphere, the method of cylindrical phase screen was developed many years ago. In this paper, we propose a further generalization of this method for the 3D problem on the basis of spherical phase screens. In the paraxial approximation, we derive the formula for the vacuum screen-to-screen propagator. We also infer the expression for the phase thickness of a thin layer of aisotropic random media. We describe a numerical implementation of this method and give numerical examples of its application for modeling a diverging laser beam propagating on a 25-km-long atmospheric path.

Method of spherical phase screens for the modeling of propagation of diverging beams in inhomogeneous media

Abstract: The phase-screen (split-step) method is widely used for the modeling of wave propagation in inhomogeneous media. Most known is the method of flat phase screens. An optimized approach based on cylindrical phase screen was introduced for the 2-D modeling of radio occultation sounding of the Earth’s atmosphere. In this paper, we propose a further generalization of this method for the 3-D problem of propagation of diverging beams. Our generalization is based on spherical phase screens. In the paraxial approximation, we derive the formula for the vacuum screen- to-screen propagator. We also derive the expression for the phase thickness of a thin layer of an isotropic random media. We describe a numerical implementation of this method and give numerical examples of its application for the modeling of a diverging laser beam propagating on a 25 km long atmospheric path.

Asymptotic iteration method for eigenvalue problems

Abstract: An asymptotic interation method for solving second-order homogeneous linear differential equations of the form y'' = lambda(x) y' + s(x) y is introduced, where lambda(x) eq 0 and s(x) are C-infinity functions. Applications to Schroedinger type problems, including some with highly singular potentials, are presented.

A cryofuge for cold-collision experiments with slow polar molecules

Abstract: Ultracold molecules represent a fascinating research frontier in physics and chemistry, but it has proven challenging to prepare dense samples at low velocities. Here we present a solution to this goal by a non-conventional approach dubbed cryofuge. It employs centrifugal force to bring cryogenically cooled molecules to kinetic energies below $1\,$K$\times k_B$ in the laboratory frame, with corresponding fluxes exceeding $10^{10}$/s at velocities below $20\,$m/s. By attaining densities higher than $10^9$/cm$^3$ and interaction times longer than $25\,$ms in samples of fluoromethane as well as deuterated ammonia, we observe cold dipolar collisions between molecules and determine their collision cross sections.

Ultracold atom-atom collisions in a nonresonant laser field

Abstract: Using a recently developed approach for treating the three-dimensional anisotropic scattering we find considerable influence of a nonresonant laser field with intensity I> or =10(5) W/cm(2) on the Cs-Cs ultracold collisions. Strong dependence on the laser wavelength lambda(L) is shown at the optical region as lambda(L) becomes shorter than the critical value lambda(0) approximately 3000 nm (of the atomic de Broglie wave lambda) defining the region lambda(0)< or =lambda of the s-wave domination in the absence of the external field. Dependence on the laser polarization is also essential. The found effect can be applicable for controlling atom-atom interactions at ultralow temperatures.

Anisotropic superfluidity in a dipolar Bose Gas

Abstract: We study the superfluid character of a dipolar Bose-Einstein condensate (DBEC) in a quasi-two dimensional geometry. We consider the dipole polarization to have some nonzero projection into the plane of the condensate so that the effective interaction is anisotropic in this plane, yielding an anisotropic dispersion relation. By performing direct numerical simulations of a probe moving through the DBEC, we observe the sudden onset of drag or creation of vortex-antivortex pairs at critical velocities that depend strongly on the direction of the probe's motion. This anisotropy emerges because of the anisotropic manifestation of a rotonlike mode in the system.