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V. I. Yukalov

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

At least 37 records · Page 2Linked to original sources
arXiv2024

Particle fluctuations in systems with Bose-Einstein condensate

Particle fluctuations in systems, exhibiting Bose-Einstein condensation, are reviewed in order to clarify the basic points that attract high interest and often confront misunderstanding. It is explained that the so-called ``grand canonical catastrophe", claiming the occurrence of catastrophic particle fluctuations in the condensed phase, treated by grand canonical ensemble, does not exist. What exists is the incorrect use of the grand canonical ensemble, where gauge symmetry is not broken, while the correct description of the condensed phase necessarily requires gauge symmetry breaking. The ideal Bose gas has no catastrophic condensate fluctuations, and moreover there are no condensate fluctuations at all, as soon as gauge symmetry is broken. However it does have anomalous fluctuations of uncondensed particles, which implies its instability. For interacting particles, there are no condensate fluctuations, as soon as gauge symmetry is broken, and anomalous fluctuations of uncondensed particles, when correctly calculated, do not appear. Particle fluctuations in the systems of trapped atoms are discussed. Canonical ensemble and grand canonical ensemble with broken gauge symmetry are equivalent with respect to the number of particle scaling.

cond-mat.quant-gas↗
arXiv2024

Strong-Coupling Extrapolation of Gell-Mann--Low Functions

Gell-Mann-Low functions can be calculated by means of perturbation theory and expressed as truncated series in powers of asymptotically small coupling parameters. However, it is necessary to know there behavior at finite values of the parameter and, moreover, their behavior at asymptotically large coupling parameters is also important. The problem of extrapolation of weak-coupling expansions to the region of finite and even infinite coupling parameters is considered. A method is suggested allowing for such an extrapolation. The basics of the method are described and illustrations of its applications are given for the examples where its accuracy and convergence can be checked. It is shown that in some cases the method allows for the exact reconstruction of the whole functions from their weak-coupling asymptotic expansions. Gell-Mann-Low functions in multicomponent field theory, quantum electrodynamics, and quantum chromodynamics are extrapolated to their strong-coupling limits.

hep-ph↗
arXiv2024

Atom Optics with Cold Bosons

Trapped bosonic atoms can be cooled down to temperatures where the atomic cloud experiences Bose-Einstein condensation. Almost all atoms in a dilute gaseous system can be Bose-condensed, which implies that this system is in a coherent state. The coherent atomic system enjoys many properties typical of coherent optical systems. It is possible to generate different condensate coherent modes similarly to the generation of optical modes. Several effects can be observed, such as interference patterns, interference current, Rabi oscillations, harmonic generation, parametric conversion, Ramsey fringes, mode locking, dynamic transition between Rabi and Josephson regimes, and atomic squeezing.

cond-mat.quant-gas↗
arXiv2024

Regulating spin dynamics of dipolar and spinor atoms

Systems of atoms or molecules can possess nonzero total spins that can be employed in spintronics, for instance for creating memory devices, which requires to be able to efficiently regulate spin directions. This article presents some methods of regulating spin dynamics, developed by the authors. These methods can be applied for different physical systems, described by different Hamiltonians including the interactions of spins with magnetic fields. The principal feature of the methods is the use of the feedback fields formed by moving spins.

cond-mat.mes-hall↗
arXiv2024

Strong-coupling limits induced by weak-coupling expansions

A method is described for the extrapolation of perturbative expansions in powers of asymptotically small coupling parameters or other variables onto the region of finite variables and even to the variables tending to infinity. The method involves the combination of ideas from renormalization group theory, approximation theory, dynamical theory, and optimal control theory. The extrapolation is realized by means of self-similar factor approximants, whose control parameters can be uniquely defined. The method allows to find the large-variable behavior of sought functions knowing only their small-variable expansions. Convergence and accuracy of the method are illustrated by explicit examples, including the so-called zero-dimensional field theory and anharmonic oscillator. Strong-coupling behavior of Gell-Mann-Low functions in multicomponent field theory, quantum electrodynamics, and quantum chromodynamics is found, being based on their weak-coupling perturbative expansions.

hep-ph↗
arXiv2023

Optimized Self-Similar Borel Summation

The method of Fractional Borel Summation is suggested in conjunction with self-similar factor approximants. The method used for extrapolating asymptotic expansions at small variables to large variables, including the variables tending to infinity, is described. The method is based on the combination of optimized perturbation theory, self-similar approximation theory, and Borel-type transformations. General Borel Fractional transformation of the original series is employed. The transformed series is resummed in order to adhere to the asymptotic power laws. The starting point is the formulation of dynamics in the approximations space by employing the notion of self-similarity. The flow in the approximation space is controlled, and ``deep'' control is incorporated into the definitions of the self-similar approximants. The class of self-similar approximations, satisfying, by design, the power law behavior, such as the use of self-similar factor approximants, is chosen for the reasons of transparency, explicitness, and convenience. A detailed comparison of different methods is performed on a rather large set of examples, employing self-similar factor approximants, self-similar iterated root approximants, as well as the approximation technique of self-similarly modified Pade - Borel approximations.

nlin.CD↗
arXiv2023

Trapped Bose-Einstein condensates with nonlinear coherent modes

The review presents the methods of generation of nonlinear coherent excitations in strongly nonequilibrium Bose-condensed systems of trapped atoms and their properties. Non-ground-state Bose-Einstein condensates are represented by nonlinear coherent modes. The principal difference of nonlinear coherent modes from linear collective excitations is emphasized. Methods of generating nonlinear modes and the properties of the latter are described. Matter-wave interferometry with coherent modes is discussed, including such effects as interference patterns, internal Josephson current, Rabi oscillations, Ramsey fringes, harmonic generation, and parametric conversion. Dynamic transition between mode-locked and mode-unlocked regimes is shown to be analogous to a phase transition. Atomic squeezing and entanglement in a lattice of condensed atomic clouds with coherent modes are considered. Nonequilibrium states of trapped Bose-condensed systems, starting from weakly nonequilibrium state, vortex state, vortex turbulence, droplet or grain turbulence, and wave turbulence, are classified by means of effective Fresnel and Mach numbers. The inverse Kibble-Zurek scenario is described. A method for the formation of directed beams from atom lasers is reported.

cond-mat.quant-gas↗
arXiv2023

Regulating spin dynamics in magnetic nanomaterials

Magnetic nanomaterials can be used in the construction of devices for information processing and memory storage. For this purpose, they have to enjoy two contradictory properties, from one side being able of keeping for long time magnetization frozen, hence information stored, and from the other side allowing for quick change of magnetization required for fast erasing of memory and rewriting new information. Methods of resolving this dilemma are suggested based on triggering resonance, dynamic resonance tuning, and on quadratic Zeeman effect. These methods make it possible to realize effective regulation of spin dynamics in such materials as magnetic nanomolecules and magnetic nanoclusters.

cond-mat.mes-hall↗
arXiv2023

Discrete Versus Continuous Algorithms in Dynamics of Affective Decision Making

The dynamics of affective decision making is considered for an intelligent network composed of agents with different types of memory: long-term and short-term memory. The consideration is based on probabilistic affective decision theory, which takes into account the rational utility of alternatives as well as the emotional alternative attractiveness. The objective of this paper is the comparison of two multistep operational algorithms of the intelligent network: one based on discrete dynamics and the other on continuous dynamics. By means of numerical analysis, it is shown that, depending on the network parameters, the characteristic probabilities for continuous and discrete operations can exhibit either close or drastically different behavior. Thus, depending on which algorithm is employed, either discrete or continuous, theoretical predictions can be rather different, which does not allow for a uniquely defined description of practical problems. This finding is important for understanding which of the algorithms is more appropriate for the correct analysis of decision-making tasks. A discussion is given, revealing that the discrete operation seems to be more realistic for describing intelligent networks as well as affective artificial intelligence.

cs.AI↗
arXiv2023

Selected Topics of Social Physics: Nonequilibrium Systems

This review article is the second part of the project ``Selected Topics of Social Physics". The first part has been devoted to equilibrium systems. The present part considers nonequilibrium systems. The style of the paper combines the features of a tutorial and a review, which, from one side, makes it easy to read for nonspecialists aiming at grasping the basics of social physics, and from the other side, describes several rather recent original models containing new ideas that could be of interest to experienced researchers in the field. The present material is based on the lectures that the author had been giving during several years at the Swiss Federal Institute of Technology in Zurich (ETH Zurich).

q-bio.PE↗
arXiv2023

Selected Topics of Social Physics: Equilibrium Systems

The present review is based on the lectures that the author had been giving during several years at the Swiss Federal Institute of Technology in Zurich (ETH Zurich). Being bounded by lecture frames, the selection of the material, by necessity, is limited and is motivated by the author's research interests. The paper gives an introduction to the physics of social systems, providing the main definitions and notions used in the modeling of these systems. The behavior of social systems is illustrated by several simple typical models. The present part considers equilibrium systems. Nonequilibrium systems will be presented in the second part of the lectures. The style of the paper combines the features of a tutorial and a survey, which, from one side, makes it easy to read for nonspecialists aiming at grasping the basics of social physics, and from the other side, describes several rather recent original models containing new ideas that could be of interest to experienced researchers in the field.

physics.soc-ph↗
arXiv2023

Quantum Operation of Affective Artificial Intelligence

The review analyzes the fundamental principles which Artificial Intelligence should be based on in order to imitate the realistic process of taking decisions by humans experiencing emotions. Two approaches are compared, one based on quantum theory and the other employing classical terms. Both these approaches have a number of similarities, being principally probabilistic. The analogies between quantum measurements under intrinsic noise and affective decision making are elucidated. It is shown that cognitive processes have many features that are formally similar to quantum measurements. This, however, in no way means that for the imitation of human decision making Affective Artificial Intelligence has necessarily to rely on the functioning of quantum systems. Appreciating the common features between quantum measurements and decision making helps for the formulation of an axiomatic approach employing only classical notions. Artificial Intelligence, following this approach, operates similarly to humans, by taking into account the utility of the considered alternatives as well as their emotional attractiveness. Affective Artificial Intelligence, whose operation takes account of the cognition-emotion duality, avoids numerous behavioural paradoxes of traditional decision making. A society of intelligent agents, interacting through the repeated multistep exchange of information, forms a network accomplishing dynamic decision making. The considered intelligent networks can characterize the operation of either a human society of affective decision makers, or the brain composed of neurons, or a typical probabilistic network of an artificial intelligence.

cs.AI↗
arXiv2023

Unified theory of quantum crystals and optical lattices with Bose-Einstein condensate

When interactions between particles are strong, at low temperature, these particles can form self-organized quantum crystals, and when the particles interact weakly, periodic structures can be imposed by external fields, e.g. by optical lattices. These opposite cases usually are treated separately, dealing either with quantum crystals or with optical lattices. Here the unified theory is developed for arbitrary particle interaction strength, treating in the frame of the same model both the limiting cases of quantum crystals and optical lattices, as well as the states intermediate between these two limits. Bose particles are considered, hence at low temperature in optical lattices Bose-Einstein condensation can happen, while it seems to be prohibited in ideal quantum crystals that do not contain mesoscopic regions of disorder, such as dislocations and grain boundaries.

cond-mat.stat-mech↗
arXiv2023

Models of Mixed Matter

The review considers statistical systems composed of several phases that are intermixed in space at mesoscopic scale and systems representing a mixture of several components of microscopic objects. These types of mixtures should be distinguished from the Gibbs phase mixture, where the system is filled by macroscopic pieces of phases. The description of the macroscopic Gibbs mixture is rather simple, consisting in the consideration of pure phases separated by a surface, whose contribution becomes negligible in thermodynamic limit. The properties of mixtures, where phases are intermixed at mesoscopic scale, are principally different. The emphasis in the review is on the matter with phases mixed at mesoscopic scale. Heterogeneous materials composed of mesoscopic mixtures are ubiquitous in nature. A general theory of such mesoscopic mixtures is presented and illustrated by several condensed matter models. A mixture of several components of microscopic objects is illustrated by clustering quark-hadron matter.

cond-mat.stat-mech↗
arXiv2023

Calibration of Quantum Decision Theory: Aversion to Large Losses and Predictability of Probabilistic Choices

We present the first calibration of quantum decision theory (QDT) to a dataset of binary risky choice. We quantitatively account for the fraction of choice reversals between two repetitions of the experiment, using a probabilistic choice formulation in the simplest form without model assumption or adjustable parameters. The prediction of choice reversal is then refined by introducing heterogeneity between decision makers through their differentiation into two groups: ``majoritarian'' and ``contrarian'' (in proportion 3:1). This supports the first fundamental tenet of QDT, which models choice as an inherent probabilistic process, where the probability of a prospect can be expressed as the sum of its utility and attraction factors. We propose to parameterise the utility factor with a stochastic version of cumulative prospect theory (logit-CPT), and the attraction factor with a constant absolute risk aversion (CARA) function. For this dataset, and penalising the larger number of QDT parameters via the Wilks test of nested hypotheses, the QDT model is found to perform significantly better than logit-CPT at both the aggregate and individual levels, and for all considered fit criteria for the first experiment iteration and for predictions (second ``out-of-sample'' iteration). The distinctive QDT effect captured by the attraction factor is mostly appreciable (i.e., most relevant and strongest in amplitude) for prospects with big losses. Our quantitative analysis of the experimental results supports the existence of an intrinsic limit of predictability, which is associated with the inherent probabilistic nature of choice. The results of the paper can find applications both in the prediction of choice of human decision makers as well as for organizing the operation of artificial intelligence.

cs.AI↗
arXiv2023

Statistical model of a superfluid solid

A microscopic statistical model of a quantum solid is developed, where inside a crystalline lattice there can exist regions of disorder, such as dislocation networks or grain boundaries. The cores of these regions of disorder are allowed for exhibiting fluid-like properties. If the solid is composed of Bose atoms, then the fluid-like aggregations inside the regions of disorder can exhibit Bose-Einstein condensation and hence superfluidity. The regions of disorder are randomly distributed throughout the sample, so that for describing the overall properties of the solid requires to accomplish averaging over the disordered aggregation configurations. The averaging procedure results in a renormalized Hamiltonian of a solid that can combine the properties of a crystal and superfluidity. The possibility of such a combination depends on the system parameters. In general, there exists a range of the model parameters allowing for the occurrence of superfluidity inside the disordered aggregations. This microscopic statistical model gives the opportunity to answer which real quantum crystals can exhibit the property of superfluidity and which cannot.

cond-mat.stat-mech↗
arXiv2022

Method of dynamic resonance tuning in spintronics of nanosystems

A method is advanced allowing for fast regulation of magnetization direction in magnetic nanosystems. The examples of such systems are polarized nanostructures, magnetic nanomolecules, magnetic nanoclusters, magnetic graphene, dipolar and spinor trapped atoms, and quantum dots. The emphasis in the paper is on magnetic nanomolecules and nanoclusters. The method is based on two principal contrivances: First, the magnetic sample is placed inside a coil of a resonant electric circuit creating a feedback field, and second, there is an external magnetic field that can be varied so that to dynamically support the resonance between the Zeeman frequency of the sample and the natural frequency of the circuit during the motion of the sample magnetization. This method can find applications in the production of memory devices and other spintronic appliances.

physics.app-ph↗
arXiv2022

Stability of normal quantum-fluid mixtures

Mixtures of quantum fluids, that is gases or liquids, are considered with the emphasis on the conditions characterizing the stability of the mixtures. The mixtures, that can be formed by cold atoms or molecules, are assumed to be quantum requiring the description using quantum techniques, but not so cold that to exhibit superfluidity or superconductivity. Reviewing the stability conditions of such normal quantum systems is important for the comparison of these conditions with the stability conditions of, e.g., Bose-condensed mixtures. The behavior of observable quantities under the stratification of quantum mixtures is discussed.

cond-mat.stat-mech↗