Beyond-Mean-Field Effects in Rabi-Coupled Two-Component Bose-Einstein Condensate.

We theoretically calculate and experimentally measure the beyond-mean-field (BMF) equation of state in a coherently coupled two-component Bose-Einstein condensate (BEC) in the regime where averaging of the interspecies and intraspecies coupling constants over the hyperfine composition of the single-particle dressed state predicts the exact cancellation of the two-body interaction. We show that with increasing the Rabi-coupling frequency Ω, the BMF energy density crosses over from the nonanalytic Lee-Huang-Yang scaling ∝n^{5/2} to an expansion in integer powers of density, where, in addition to a two-body BMF term ∝n^{2}sqrt[Ω], there emerges a repulsive three-body contribution ∝n^{3}/sqrt[Ω]. We experimentally evidence these two contributions, thanks to their different scaling with Ω, in the expansion of a Rabi-coupled two-component ^{39}K condensate in a waveguide. By studying the expansion with and without Rabi coupling, we reveal an important feature relevant for observing BMF effects and associated phenomena in mixtures with spin-asymmetric losses: Rabi coupling helps preserve the spin composition and thus prevents the system from drifting away from the point of the vanishing mean field.

[The medical social problems and methods of diagnostic of cognitive disorders in patients taking "Spice"].

The article presents the results of pilot study implemented to determine cognitive disorders in patients taking "Spice". The purpose of research is to identify targets of psychological correction interventions to prevent cognitive deficiency in patients addicted to synthetic cannabinoids. The pilot sampling consisted of 30 patients taking "Spice". The control group consisted of 30 healthy individuals. Along with social consequences, one of the important focuses of the study was investigation of cognitive sphere of patients. A number of pathopsychologic tests was applied. The study established that patients demonstrated disorders of various functions of memory, attention, mental pace and thinking. In particular, disorders of short-term, long-term and mediate memory and mental tempo were revealed. Also, reduced activity of attention took place. The distortion and decreasing of generalization and poor prehension occurred reliably more often as compared with control group. The established cognitive disorders in patients taking "Spice" can be considered as targets for psychological correction interventions to prevent cognitive deficiency in patients addicted to synthetic cannabinoids.

[The mental reactions of psychiatrists and narcologists against the background of COVID-19 pandemic].

The article considers various mental reactions of psychiatrists and narcologists against the background of the SARS-CoV-2 pandemic, based on a brief scientific analysis of publications and experimental psychological research methods. The purpose of study was to identify impact of the COVID-19 pandemic on mental health of psychiatrists and psychiatrists-narcologists. The results of survey of psychiatrists and narcologists are presented. The study was carried out using such test techniques as life quality scale SF-36 (Health Status Survey), Lazarus questionnaire "Coping Behaviors" adjusted to conditions of Russia and Hamilton scales to assess depression and anxiety (HDRS, HARS). The results.The low level of psychological well-being, moderate degree of preference for all coping strategies were established. The anxiety was determine in 34.8% of respondents and depression in 8.7%. It was established that actually, the impact of the COVID-19 pandemic on medical workers is conditioned by complex of mental reactions (from anosognosia to expressed anxiety and depressive disorders) and is accompanied by increasing general anxiety.

[The analysis of failures of intra-familial relationships in families with children suffering of diabetes mellitus].

The article presents the results of study of in-family (child-parents) relationships in families with children suffering with diagnosed diabetes mellitus type I. The purpose of study is to investigate the disorders of family relationships in families of such kind. The established disorders allow to develop psychotherapeutic measures both for children and their parents. Materials and methods. The study covered 30 families with children of primary school age (7-10 years old) with diabetes mellitus. The families with children with severe concomitant diseases and broken families were excluded of the sampling. The control group consisted of 30 relevant families with healthy children. The in-family relationships were explored using a number of psychological tests applied to children and their mothers. The results. In mothers of the studied families prevailed authoritarian type of upbringing, which was expressed in tendency to hyper-protect and to over-control. The phobia of losing child and the tendency to reject it were also established. The children suffered from high level of anxiety. They had more positive attitude to mother than to father. The conclusion. The established disorders of in-family relationships in families with children with diabetes mellitus can serve as targets for psychotherapeutic activities both with children and their parents.

Mixed Bubbles in Bose-Bose Mixtures.

Repulsive Bose-Bose mixtures are known to either mix or phase separate into pure components. Here we predict a mixed-bubble regime in which bubbles of the mixed phase coexist with a pure phase of one of the components. This is a beyond-mean-field effect that occurs for unequal masses or unequal intraspecies coupling constants and is due to a competition between the mean-field term, quadratic in densities, and a nonquadratic beyond-mean-field correction. We find parameters of the mixed-bubble regime in all dimensions and discuss implications for current experiments.

Stable p-Wave Resonant Two-Dimensional Fermi-Bose Dimers.

We consider two-dimensional weakly bound heterospecies molecules formed in a Fermi-Bose mixture with attractive Fermi-Bose and repulsive Bose-Bose interactions. Bosonic exchanges lead to an intermolecular attraction, which can be controlled and tuned to a p-wave resonance. Such attractive fermionic molecules can be realized in quasi-two-dimensional ultracold isotopic mixtures. We show that they are stable with respect to the recombination to deeply bound molecular states and with respect to the formation of higher-order clusters (trimers, tetramers, etc.).

Five-Body Efimov Effect and Universal Pentamer in Fermionic Mixtures.

We show that four heavy fermions interacting resonantly with a lighter atom (4+1 system) become Efimovian at mass ratio 13.279(2), which is smaller than the corresponding 2+1 and 3+1 thresholds. We thus predict the five-body Efimov effect for this system in the regime where any of its subsystem is non-Efimovian. For smaller mass ratios we show the existence and calculate the energy of a universal 4+1 pentamer state, which continues the series of the 2+1 trimer predicted by Kartavtsev and Malykh and 3+1 tetramer discovered by Blume. We also show that the effective-range correction for the light-heavy interaction has a strong effect on all these states and larger effective ranges increase their tendency to bind.

Anisotropic Expansion of a Thermal Dipolar Bose Gas.

We report on the anisotropic expansion of ultracold bosonic dysprosium gases at temperatures above quantum degeneracy and develop a quantitative theory to describe this behavior. The theory expresses the postexpansion aspect ratio in terms of temperature and microscopic collisional properties by incorporating Hartree-Fock mean-field interactions, hydrodynamic effects, and Bose-enhancement factors. Our results extend the utility of expansion imaging by providing accurate thermometry for dipolar thermal Bose gases. Furthermore, we present a simple method to determine scattering lengths in dipolar gases, including near a Feshbach resonance, through observation of thermal gas expansion.

Ultradilute Low-Dimensional Liquids.

We calculate the energy of one- and two-dimensional weakly interacting Bose-Bose mixtures analytically in the Bogoliubov approximation and by using the diffusion Monte Carlo technique. We show that in the case of attractive inter- and repulsive intraspecies interactions the energy per particle has a minimum at a finite density corresponding to a liquid state. We derive the Gross-Pitaevskii equation to describe droplets of such liquids and solve it analytically in the one-dimensional case.

Quantum Mechanical Stabilization of a Collapsing Bose-Bose Mixture.

According to the mean-field theory a condensed Bose-Bose mixture collapses when the interspecies attraction becomes stronger than the geometrical average of the intraspecies repulsions, g_{12}^{2}>g_{11}g_{22}. We show that instead of collapsing such a mixture gets into a dilute liquidlike droplet state stabilized by quantum fluctuations thus providing a direct manifestation of beyond mean-field effects. We study various properties of the droplet and find, in particular, that in a wide range of parameters its excitation spectrum lies entirely above the particle emission threshold. The droplet thus automatically evaporates itself to zero temperature, the property potentially interesting by itself and from the viewpoint of sympathetic cooling of other systems.

Stable Dilute Supersolid of Two-Dimensional Dipolar Bosons.

We consider two-dimensional bosonic dipoles oriented perpendicularly to the plane. On top of the usual two-body contact and long-range dipolar interactions we add a contact three-body repulsion as expected, in particular, for dipoles in the bilayer geometry with tunneling. The three-body repulsion is crucial for stabilizing the system, and we show that our model allows for stable continuous space supersolid states in the dilute regime and calculate the zero-temperature phase diagram.

Three-body interacting bosons in free space.

We propose a method of controlling two- and three-body interactions in an ultracold Bose gas in any dimension. The method requires us to have two coupled internal single-particle states split in energy such that the upper state is occupied virtually but amply during collisions. By varying system parameters, one can switch off the two-body interaction while maintaining a strong three-body one. The mechanism can be implemented for dipolar bosons in the bilayer configuration with tunneling or in an atomic system by using radio-frequency fields to couple two hyperfine states. One can then aim to observe a purely three-body interacting gas, dilute self-trapped droplets, the paired superfluid phase, Pfaffian state, and other exotic phenomena.

Lifetime of the Bose gas with resonant interactions.

We study the lifetime of a Bose gas at and around unitarity using a Feshbach resonance in lithium 7. At unitarity, we measure the temperature dependence of the three-body decay coefficient L(3). Our data follow a L(3)=λ(3)/T(2) law with λ(3)=2.5(3)(stat)(6)(syst)×10(-20) (µK)(2) cm(6) s(-1) and are in good agreement with our analytical result based on zero-range theory. Varying the scattering length a at fixed temperature, we investigate the crossover between the finite-temperature unitary region and the previously studied regime where |a| is smaller than the thermal wavelength. We find that L(3) is continuous across the resonance, and over the whole a<0 range our data quantitatively agree with our calculation.

Parametric excitation of a 1D gas in integrable and nonintegrable cases.

We study the response of a highly excited 1D gas with pointlike interactions to a periodic modulation of the coupling constant. We calculate the corresponding dynamic structure factors and show that their low-frequency behavior differs dramatically for integrable and nonintegrable models. Nonintegrable systems are sensitive to excitations with frequencies as low as the mean level spacing, whereas much higher frequencies are required to excite an integrable system. This effect can be used as a probe of integrability for mesoscopic 1D systems and can be observed experimentally by measuring the heating rate of a parametrically excited gas.

[The medical social characteristic of patients with psychic disorders addressed to medical institutions with various forms of property].

The article deals with the issues of enhancement of the psychiatric service. The analysis of the results of medical social study of the patients addressed for the medical care to public and commercial structures is given. The substantiation of necessity in enhancing the quality and effectiveness of out-patient psychiatric care service are presented and the various alternative models of its development as well.

Atom-dimer scattering and long-lived trimers in fermionic mixtures.

We consider a heteronuclear fermionic mixture on the molecular side of an interspecies Feshbach resonance and discuss atom-dimer scattering properties in uniform space and in the presence of an external confining potential, restricting the system to a quasi-two-dimensional geometry. We find that there is a peculiar atom-dimer p-wave resonance which can be tuned by changing the frequency of the confinement. Our results have implications for the ongoing experiments on lithium-potassium mixtures, where this mechanism allows for switching the p-wave interaction between a K atom and Li-K dimer from attractive to repulsive, and forming a weakly bound trimer with unit angular momentum. We show that such trimers are long lived and the atom-dimer resonance does not enhance inelastic relaxation in the mixture, making it an outstanding candidate for studies of p-wave resonance effects in a many-body system.

Crystalline phase of strongly interacting fermi mixtures.

We show that the system of weakly bound molecules of heavy and light fermionic atoms is characterized by a long-range intermolecular repulsion and can undergo a gas-crystal quantum transition if the mass ratio exceeds a critical value. For the critical mass ratio above 100 obtained in our calculations, this crystalline order can be observed as a superlattice in an optical lattice for heavy atoms with a small filling factor. We also find that this novel system is sufficiently stable with respect to molecular relaxation into deep bound states and to the process of trimer formation.

Three-boson problem near a narrow Feshbach resonance.

We consider a three-boson system with resonant binary interactions and show that for sufficiently narrow resonances three-body observables depend only on the resonance width and the scattering length. The effect of narrow resonances is qualitatively different from that of wide resonances revealing novel physics of three-body collisions. We calculate the rate of three-body recombination to a weakly bound level and the atom-dimer scattering length and discuss implications for experiments on Bose-Einstein condensates and atom-molecule mixtures near Feshbach resonances.

Weakly bound dimers of fermionic atoms.

We discuss the behavior of weakly bound bosonic dimers formed in a two-component cold Fermi gas at a large positive scattering length a for the interspecies interaction. We find the exact solution for the dimer-dimer elastic scattering and obtain a strong decrease of their collisional relaxation and decay with increasing a. The large ratio of the elastic to inelastic rate is promising for achieving Bose-Einstein condensation of the dimers and cooling the condensed gas to very low temperatures.