arXiv subjects

V. I. Yukalov

Publications and source records attributed to V. I. Yukalov.

At least 289 records · Page 16Linked to original sources

arXiv2001

Dynamic Critical Phenomena in Trapped Bose Gases

Nonlinear dynamics of a trapped Bose-Einstein condensate, subject to the action of a resonant external field, is studied. This field produces a spatio-temporal modulation of the trapping potential with the frequency close to the transition frequency between the ground state and a higher energy level. The evolution equations of fractional populations display a kind of critical phenomena at a critical line on the manifold of the system parameters. It is demonstrated that there exists a direct analogy between dynamical instability at this line and critical phenomena at a critical line of a related averaged system.

cond-mat↗

arXiv2001

Crystal Symmetry and Time Scales

The relation between the notion of crystalline symmetry and characteristic time intervals when this symmetry could be observed is analyzed. Several time scales are shown to exist for a system of interacting particles. It is only when the observation time is much larger than the mesoscopic fluctuation time, the notion of crystalline symmetry becomes physically meaningful. The ideas are concretized by a two-phase lattice model.

cond-mat↗

arXiv2001

Nonground State Condensates of Ultracold Trapped Atoms

The population dynamics of a trapped Bose-Einstein condensate, subject to the action of an oscillatory field, is studied. This field produces a modulation of the trapping potential with the frequency close to the transition frequency between the ground state and an excited energy level. Unusual critical effects are found exhibiting sharp qualitative changes in the population dynamics. An effective averaged system is constructed explicitly illustrating the occurrence of critical phenomena. The related critical indices are calculated.

cond-mat↗

arXiv2001

Enhancement of Nuclear Spin Superradiance by Electron Resonator

Superradiance of nuclear spins is considered, when the nuclei interact via hyperfine forces with electrons of a ferromagnet. The consideration is based on a microscopic model. If the sample, coupled with a resonant electric circuit, possesses electronic magnetization, then the electron subsystem plays the role of an additional effective resonator, by enhancing the coupling between nuclear spins and the resonant circuit. Radiation power can be increased by three orders, while the radiation time of a superradiance burst can become three times shorter. In the presence of dynamic nuclear polarization, the regime of pulsing superradiance can occur.

cond-mat↗

arXiv2001

Probabilistic Approach to Pattern Selection

The problem of pattern selection arises when the evolution equations have many solutions, whereas observed patterns constitute a much more restricted set. An approach is advanced for treating the problem of pattern selection by defining the probability distribution of patterns. Then the most probable pattern naturally corresponds to the largest probability weight. This approach provides the ordering principle for the multiplicity of solutions explaining why some of them are more preferable than other. The approach is applied to solving the problem of turbulent photon filamentation in resonant media.

cond-mat↗

arXiv2001

Coherent Effects under Suppressed Spontaneous Emission

An ensemble of resonance atoms is considered, which are doped into a medium with well developed polariton effect, when in the spectrum of polariton states there is a band gap. If an atom with a resonance frequency inside the polariton gap is placed into the medium, the atomic spontaneous emission is suppressed. However, a system of resonance atoms inside the polariton gap can radiate when their coherent interaction is sufficiently strong. Thus the suppression of spontaneous emission for a single atom can be overcome by a collective of atoms radiating coherently. Conditions when such collective effects can appear and their dynamics are analysed.

cond-mat↗

arXiv2001

Self-Similar Extrapolation of Asymptotic Series and Forecasting for Time Series

The method of extrapolating asymptotic series, based on the Self-Similar Approximation Theory, is developed. Several important questions are answered, which makes the foundation of the method unambiguous and its application straightforward. It is shown how the extrapolation of asymptotic series can be reformulated as forecasting for time series. The probability measure is introduced characterizing the ensemble of forecasted scenarios. The way of choosing the complete family of data bases is advanced.

cond-mat↗

arXiv2001

Turbulent Photon Filamentation in Resonant Media

Optical turbulence is the term that is used being based on the analogy between hydrodynamic and optical equations. The phenomenon of turbulent photon filamentation occurs in lasers and other active optical media at high Fresnel numbers. A description of this phenomenon is suggested. The solutions to evolution equations are presented in the form of a bunch of filaments chaotically distributed in space and having different radii. The probability distribution of patterns is defined characterizing the probabilistic weight of different filaments. The most probable filament radius and filament number are found, being in good agreement with experiment.

cond-mat↗

arXiv2000

Cooperative Electromagnetic Effects

Collective phenomena in strongly nonequilibrium systems interacting with electromagnetic field are considered. Such systems are described by complicated nonlinear differential or integro-differential equations. The aim of this review is to show that many nonlinear collective phenomena can be successfully treated by a recently developed method called the Scale Separation Approach whose name is due to the idea of separating different characteristic space-time scales existing in nonequilibrium statistical systems. This approach is rather general and can be applied to various nonequilibrium physical problems, several of which are discussed here. The problems considered not only serve as illustrations of the method but are quite important by themselves presenting interesting physical effects, such as Collective Liberation of Light, Turbulent Photon Filamentation, Superradiant Spin Relaxation, Negative Electric Current, and Magnetic Semiconfinement of Atoms.

cond-mat↗

arXiv2000

Equation of State in Quantum Chromodynamics

The equation of state for quark-gluon plasma is obtained, being valid for arbitrary values of the coupling parameter and of temperature. This equation is constructed from perturbative expansions for free energy and for renormalization function. Summation of asymptotic perturbative series is accomplished by means of the self-similar approximation theory.

hep-ph↗

arXiv2000

Coherent Optics and Localized Light

Interplay between the effects of coherent radiation and localization of light is analysed. A system of two-level atoms is placed in a medium interacting with electromagnetic field. The matter-light interaction can result in the appearance of a band gap in the spectrum of polariton states. If an atom with a resonance frequency inside the gap is incorporated into such a medium, the atomic spontaneous emission is suppressed, which is termed the localization of light. However, a system of resonance atoms inside the gap can radiate due to their coherent interactions. The peculiarity of the coherent radiation by a system of atoms, under the localization of light for a single atom, is studied.

quant-ph↗

arXiv2000

Excited Coherent Modes of Ultracold Trapped Atoms

A method of exciting coherent spatial modes of Bose-condensed trapped atoms is considered. The method is based on the resonance modulation of the trapping potential. The population dynamics of coherent modes is analysed. The method makes it possible to create mixtures of different spatial modes in arbitrary proportions, including the formation of pure excited coherent modes. Novel critical effects in the population dynamics are found.

cond-mat↗

arXiv2000

Formation of Directed Beams from Atom Lasers

The problem of creating well-collimated beams of atoms escaping from a trap is studied. This problem is of high importance for the realization of atom lasers. Nonadiabatic dynamics of neutral atoms in nonuniform magnetic fields, typical of quadrupole magnetic traps, has been considered. The main result of this report is that an unusual semiconfining regime of motion is found, when atoms are confined from one side of an axis but are not confined from another side. This regime can be achieved by means of only magnetic fields. The formed atomic beam can be forwarded in arbitrary direction.

cond-mat↗

arXiv2000

Collective Phenonema in the Interaction of Radiation with Matter

The aim of this communication is to present in a concentrated form the main ideas of a method, developed by the author, for treating strongly nonequilibrium collective phenomena typical of the interaction of radiation with matter, as well as to give a survey of several applications of the method. The latter is called the Scale Separation Approach since its basic techniques rely on the possibility of separating different space-time scales in nonequilibrium statistical systems. This approach is rather general and can be applied to diverse physical problems, several of which are discussed here. These problems are: Superradiance of nuclear spins, filamentation in resonant media, semiconfinement of neutral atoms, negative electric current, and collective liberation of light.

cond-mat↗

arXiv2000

Ion-Beam Induced Current in High-Resistance Materials

The peculiarities of electric current in high-resistance materials, such as semiconductors or semimetals, irradiated by ion beams are considered. It is shown that after ion--beam irradiation an unusual electric current may arise directed against the applied voltage. Such a negative current is a transient effect appearing at the initial stage of the process. The possibility of using this effect for studying the characteristics of irradiated materials is discussed. A new method for defining the mean projected range of ions is suggested.

cond-mat↗

arXiv2000

Self-Similar Crossover in Statistical Physics

An analytical method is advanced for constructing interpolation formulae for complicated problems of statistical mechanics, in which just a few terms of asymptotic expansions are available. The method is based on the self-similar approximation theory, being its variant where control functions are defined from asymptotic crossover conditions. Several examples from statistical physics demonstrate that the suggested method results in rather simple and surprisingly accurate formulae.

cond-mat↗

arXiv1999

Self-Similar Perturbation Theory

A method is suggested for treating those complicated physical problems for which exact solutions are not known but a few approximation terms of a calculational algorithm can be derived. The method permits one to answer the following rather delicate questions: What can be said about the convergence of the calculational procedure when only a few its terms are available and how to decide which of the initial approximations of the perturbative algorithm is better, when several such initial approximations are possible? Definite answers to these important questions become possible by employing the self-similar perturbation theory. The novelty of this paper is in developing the stability analysis based on the method of multipliers and in illustrating the efficiency of this analysis by different quantum-mechanical problems.

hep-ph↗

arXiv1999

Transient Effect of Negative Electric Current in Irradiated Semiconductors

The peculiarities of electric current are studied occurring in semiconductors with strongly nonuniform distribution of charge carriers. The formation of such nonuniformities and the regulation of carrier mobilities can be realized by means of external irradiation, for instance, charge-particle beams and laser irradiation. The transient effect of negative electric current is shown to arise under some specific conditions.

cond-mat↗