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The investigation of atom number fluctuations in quantum gases at finite temperatures showcases the ongoing challenges in understanding complex quantum systems. Recently, the microcanonical nature of atom number fluctuations in weakly interacting Bose–Einstein condensates was observed. This motivates an investigation of the thermal component of partially condensed Bose gases, due to the conservation of the total atom number. Here, we present a combined analysis of both components, including a comprehensive analysis of the uncertainties in the preparation and parameter extraction of partially condensed quantum gases. This enables a complementary observation of the thermal atom number fluctuations and yields and improved value of the peak BEC atom number fluctuations Δ N p , 0 2 = (3.7 ± 7) × 10 5 close to the critical temperature. This corresponds to a reduction by 41% with respect to previous analysis and corroborates the microcanonical nature of the fluctuations. The analysis of noise contributions due to the preparation and evaluation of partially condensed Bose gases is based on Monte Carlo simulations of optical density profiles. Importantly, this allows for an estimation of the technical noise contributions to the atom number and temperature, which is generally applicable in the field of ultracold atoms. [ABSTRACT FROM AUTHOR]

We present an overview of the approach to establish a lower bound to the ground state energy for the dilute, interacting Bose gas in a periodic box. In this paper, the size of the box is larger than the Gross–Pitaevskii length scale. The presentation includes both the two- and three-dimensional cases, and catches the second-order correction, i.e. the Lee–Huang–Yang term. The calculation on a box of this length scale is the main step to calculate the energy in the thermodynamic limit. However, the periodic boundary condition simplifies many steps of the argument considerably compared to the localized problem coming from the thermodynamic case. [ABSTRACT FROM AUTHOR]

Multiple-RF (MRF) dressing allows trapping of ultracold atoms in novel spatial geometries, such as highly controllable bilayer structures for two-dimensional (2D) ultracold gases, providing unique opportunities for the investigation of 2D quantum systems both in and out of equilibrium. Here, we give an overview of the recent developments of MRF-dressed atom experiments, illustrated by the detailed studies of universal relaxation dynamics across the Berezinskii–Kosterlitz–Thouless critical point enabled by coherent splitting quench protocols and detection of correlations via spatially selective matter-wave interferometry. [ABSTRACT FROM AUTHOR]

From the time-dependent Gross equation, we find the quasiparticle dispersion law for a one-dimensional weakly interacting Bose gas with a non-point interatomic potential and zero boundary conditions (BCs). The result coincides with the dispersion law for periodic BCs, i.e., the Bogoliubov law E B (k) = ħ 2 k 2 2 m 2 + n 0 ν (k) ħ 2 k 2 m . In the case of periodic BCs, the dispersion law can be easily derived from Gross' equation. However, for zero BCs, the analysis is not so simple. [ABSTRACT FROM AUTHOR]

Quantum thermal engines have received much attention in recent years due to their potential applications. For a candidate group, harmonically trapped gases under Bose–Einstein condensation (BEC), we see little investigation on the energy transference around that transition. Therefore, we present an empirical study with rubidium-87 gas samples in a magnetic harmonic trap. We developed an empirical equation of state model to fit to our experimental dataset, expressing the pressure parameter in terms of temperature, and six technical coefficients, functions of the volume parameter and the number of atoms. By using standard thermodynamic relations, we determine the system's entropy, shown to be constant at the BEC transition, as expected. Being isentropic makes the BEC transition an energy source for non-mechanical work. Hence, we observed that the enthalpy at the BEC transition, at fixed values of the volume parameter, grows fairly linearly with the number of atoms. We fitted a linear function to that data, finding the specific enthalpy of the BEC transformation and the intrinsic enthalpic loss for BEC. We deem this study to be a step closer to practical quantum-based engines. [ABSTRACT FROM AUTHOR]

Anyons with a statistical phase parameter α ∈ (0 , 2) are a kind of quasi-particles that, for topological reasons, only exist in a 1D or 2D world. We consider the dimensional reduction for a 2D system of anyons in a tight wave guide. More specifically, we study the 2D magnetic gauge picture model with an imposed anisotropic harmonic potential that traps particles much stronger in the y-direction than in the x-direction. We prove that both the eigenenergies and the eigenfunctions are asymptotically decoupled into the loose confining direction and the tight confining direction during this reduction. The limit 1D system for the x-direction is given by the impenetrable Tonks–Girardeau Bose gas, which has no dependency on α , and no trace left of the long-range interactions of the 2D model. [ABSTRACT FROM AUTHOR]

Recent progress in out-of-equilibrium closed quantum systems has significantly advanced the understanding of mechanisms behind their evolution toward thermalization. Notably, the concept of nonthermal fixed points (NTFPs)--responsible for the emergence of spatiotemporal universal scaling in far-from-equilibrium systems--has played a crucial role in both theoretical and experimental investigations. In this work, we introduce a differential equation that has the universal scaling associated with NTFPs as a solution. The advantage of working with a differential equation, rather than only with its solution, is that we can extract several insightful properties not necessarily present in the solution alone. How the differential equation is derived allows physical interpretation of the universal exponents in terms of the time dependence of the amplitude of the distributions and their momentum scaling. Employing two limiting cases of the equation, we determined the universal exponents related to the scaling using the distributions near just two momentum values. We established a solid agreement with previous investigations by validating this approach with three distinct physical systems. This consistency highlights the universal nature of scaling due to NTFPs and emphasizes the predictive capabilities ofthe proposed differential equation. Moreover, under specific conditions, the equation predicts a power-law related to the ratio of the two universal exponents, leading to implications concerning particle and energy transport. This suggests that the observed power-laws in far-from-equilibrium turbulent fluids could be related to the universal scaling due to NTFPs, potentially offering insights into the study of turbulence. [ABSTRACT FROM AUTHOR]

This mini-review examines the optical properties of nanoheterostructures of the second type, consisting of germanium quantum dots expressed in a silicon matrix. It has been shown that the radiation intensities and the lifetimes associated with electron transitions between quasistationary states of a single germanium quantum dot, take significant values compared to similar values in germanium/silicon nanosystems. This effect will make it possible to create a new generation of efficient light-emitting devices based heterostructures with germanium quantum dots. In addition, long-lived quasistationary states will make it possible to realize high-temperature quantum Bose-gases states in the nanosystem under study. [ABSTRACT FROM AUTHOR]

We consider the ground state of Rydberg-dressed Bose gas with spin–orbit coupling and confined in a two-dimensional optical lattice. The effects of system's parameters, especially the nonlocal Rydberg interaction and spin–orbit coupling, on the ground-state structure of such a system are explored in full parameter space. It is found that in the absence of spin–orbit coupling, the ground-state structure of the system changes from the initial optical lattice structure to a two-dimensional periodic one with the cell size decreasing with the strength of Rydberg interaction. In the presence of spin–orbit coupling, both the phase and the internal structure of unit cell show strong dependence on the strength of spin–orbit coupling. Finally, the strong interacting gas is also considered. [ABSTRACT FROM AUTHOR]

Palatini-like theories of gravity have a remarkable connection to models incorporating linear generalized uncertainty principles. Considering this, we delve into the thermodynamics of systems comprising both Bose and Fermi gases. Our analysis encompasses the equations of state for various systems, including general Fermi gases, degenerate Fermi gases, Boltzmann gases, and Bose gases such as phonons and photons, as well as Bose–Einstein condensates and liquid helium. [ABSTRACT FROM AUTHOR]

Starting from a degenerate Bose gas in a hybrid trap combining a magnetic quadrupole trap and an attractive optical trap resulting from a focused laser beam, we demonstrate the efficient loading of this quantum gas into a shell-shaped trap. The shell trap is purely magnetic and relies on adiabatic potentials for atoms in an inhomogeneous magnetic field dressed by a radiofrequency (rf) field. We show that direct rf evaporation in the hybrid trap enables an efficient and simple preparation of the cold sample, well adapted to the subsequent loading procedure. The transfer into the shell trap is adiabatic and limits the final excitation of the center-of-mass motion to below 2 μ m. [ABSTRACT FROM AUTHOR]

We study the effects of dipole–dipole interactions on the diffusion of an expanding atomic Bose–Einstein condensate with tunable s-wave interactions in three-dimensional disorder potentials. First-order correction due to local and nonlocal nonlinearities to the average atomic density is analytically calculated in the long expanding time limit using a perturbative theory. It is found that the diffusion coefficient exhibits a stronger anisotropy dependence due to the dipolar interactions. We show that the intriguing interplay of dipolar and nondipolar interactions and disorder potential may affect the diffusive expansion. Profiles of the dynamics of the average atomic density of attractive DDI from Eq.(19) for different values of ϵ dd and p = 0.08 . Black lines: ϵ dd = 0 . Red lines: ϵ dd = 0.16 . Blue lines: ϵ dd = 0.4 . Green lines: ϵ dd = 0.8 [ABSTRACT FROM AUTHOR]

We prove the following formula for the ground state energy density of a dilute Bose gas with density ρ in 2 dimensions in the thermodynamic limit e 2D (ρ) = 4 π ρ 2 Y (1 - Y | log Y | + (2 Γ + 1 2 + log (π)) Y) + o (ρ 2 Y 2) , as ρ a 2 → 0 . Here Y = | log (ρ a 2) | - 1 and a is the scattering length of the two-body potential. This result in 2 dimensions corresponds to the famous Lee–Huang–Yang formula in 3 dimensions. The proof is valid for essentially all positive potentials with finite scattering length, in particular, it covers the crucial case of the hard core potential. [ABSTRACT FROM AUTHOR]

We report on a numerical study of the critical velocity for creation of quantized vortices by a moving Gaussian obstacle in a trapped Bose–Einstein condensate, modeled by the Gross–Pitaevskii equation. We pay attention to impact of density inhomogeneity associated with the global inverted parabolic profile by a trapping potential as well as the local density suppression around the Gaussian obstacle. When the width of the Gaussian potential is large, the wake dynamics is significantly influenced by the nonuniformity around the obstacle potential. The critical velocity, estimated through the time interval between the first and second vortex emission, can be explained by the local sound velocity by taking into account the above two contributions. We find that the ratio of the critical velocity for vortex creation to the sound velocity at the center of the system is minimally influenced by the nonlinear coefficient in the Gross–Pitaevskii equation. This result implies that the analysis in the homogeneous system is directly applicable to the inhomogeneous trapped condensates under the local density approximation. [ABSTRACT FROM AUTHOR]

In this paper, the vortices number and the critical atoms number are calculated. Calculations are performed for ultracold trapped Bose gas in two-dimensional deep optical lattice. Hellmann–Feynman theorem is used here to calculate the expectation values of the angular momentum and thermal average of square radius (in situ size). The above-mentioned parameters are calculated from the thermodynamic grand potential q (α , s). The latter is calculated using a conventional semi-classical approximation. This thermodynamic grand potential allows us to investigate the impacts of the finite size and inter-atomic interaction effects. The obtained result for the vortices number has a peak with increase in the rate of rotation. While the critical atoms number has increase in nature with increase in the critical temperature. These parameters show a major dependence on the inter-atomic interaction, depth of optical lattice and number of particles. [ABSTRACT FROM AUTHOR]

Cold atomic gases provide a remarkable testbed to study the physics of interacting many-body quantum systems. Temperatures are necessarily nonzero, but cooling to the ultralow temperatures needed for quantum simulation purposes or even simply measuring the temperatures directly on the system can prove to be very challenging tasks. Here, we implement thermometry on strongly interacting two-and one-dimensional Bose gases with high sensitivity in the nanokelvin temperature range. Our method is aided by the fact that the decay of the first-order correlation function is very sensitive to the temperature when interactions are strong. We find that there may be a substantial temperature variation when the three-dimensional quantum gas is cut into two-dimensional slices or into one-dimensional tubes. Notably, the temperature for the one-dimensional case can be much lower than the initial temperature. Our findings show that this decrease results from the interplay of dimensional reduction and strong interactions. [ABSTRACT FROM AUTHOR]

We propose the method for numerical solution of four-wave kinetic equations that arise in the wave turbulence (weak turbulence) theory when describing a homogeneous isotropic interaction of waves. To calculate the collision integral in the right-hand side of equation, the cubature formulas of high rate of convergence are developed, which allow for adaptation of the algorithm to the singularities of the solutions and of the integral kernels. The convergence tests in the problems of integration arising from real applications are done. To take into account the multi-scale nature of turbulence problems in our algorithm, rational approximations of the solutions and a new time marching scheme are implemented and tested. The efficiency of the developed algorithm is demonstrated by modelling the inverse cascade of Bose gas particles during the formation of a Bose–Einstein condensate. [ABSTRACT FROM AUTHOR]

Black holes violate the third law of thermodynamics, and this gives rise to difficulties with the microscopic description of their entropy. Recently, it has been shown that the microscopic description of the Schwarzschild black hole thermodynamics in space–time dimensions is provided by the analytic continuation of the entropy of Bose gas with a nonrelativistic one-particle energy to negative spatial dimensions. In this paper, we show that the and Schwarzschild black holes thermodynamics can be modeled by the -dimensional Bose gas, , with the one-particle energy under the respective conditions and . In these cases, the free energy of the Bose gas has divergences, and we introduce a cut-off and perform the minimal renormalizations. We also perform renormalizations using analytic regularization and prove that the minimal cut-off renormalization gives the same answer as the analytic regularization by the Riemann zeta-function. [ABSTRACT FROM AUTHOR]

The divergence-free nature of Bessel beams can be harnessed to effectively trap optical vortices in free space laser propagation. We show how to generate arbitrary vortex configurations in Bessel traps to investigate few-body vortex interactions within a dynamically evolving fluid of light, which is a formal analog to a non-interacting Bose gas. We implement—theoretically and experimentally—initial conditions of vortex configurations first predicted in harmonically trapped quantum fluids, in the limit of weak atomic interactions, and model and measure the resultant dynamics. These hard trap dynamics are distinct from the harmonic trap predictions due to the non-local interactions that occur among the hard-wall boundary and steep phase gradients that nucleate other vortices. By simultaneously presenting experimental demonstrations with the theoretical proposal, we validate the potential application of using Bessel hard-wall traps as testing grounds for engineering few-body vortex interactions within trapped, two-dimensional compressible fluids. [ABSTRACT FROM AUTHOR]

Closed quantum systems far from thermal equilibrium can show universal dynamics near attractor solutions, known as non-thermal fixed points, generically in the form of scaling behaviour in space and time. A systematic classification and comprehensive understanding of such scaling solutions are tasks of future developments in non-equilibrium quantum many-body theory. In this tutorial review, we outline several analytical approaches to non-thermal fixed points and summarise corresponding numerical and experimental results. The analytic methods include a non-perturbative kinetic theory derived within the two-particle irreducible effective action formalism, as well as a low-energy effective field theory framework. As one of the driving forces of this research field are numerical simulations, we summarise the main results of exemplary cases of universal dynamics in ultracold Bose gases. This encompasses quantum vortex ensembles in turbulent superfluids as well as recently observed real-time instanton solutions in one-dimensional spinor condensates. [ABSTRACT FROM AUTHOR]

We characterize the energy spectrum in far-from-equilibrium inhomogeneously trapped Bose-Einstein condensate using the power spectrum technique. We demonstrate that pseudo-momentum fluctuations can be used to characterize turbulence and we compare the obtained exponents to one measured by well established techniques such as the momentum distribution in time of flight. The power spectrum of pseudo-momentum fluctuations and the momentum distribution reveals a power-law dependence into the inertial range of momentum for the turbulent out-of-equilibrium system. We analyze the evolution of the power-law exponent for different far-from-equilibrium regimes and both methods show that the power-law exponent reaches the same stationary value when the cloud is in the developed turbulent regime. These results provide a better understanding of out-of-equilibrium states, which is a new frontier in the study of cold trapped atoms. [ABSTRACT FROM AUTHOR]

We consider N trapped bosons in the mean-field limit with coupling constant λN = 1/(N − 1). The ground state of such systems exhibits Bose–Einstein condensation. We prove that the probability of finding ℓ particles outside the condensate wave function decays exponentially in ℓ. [ABSTRACT FROM AUTHOR]

Cold atomic gases have become a paradigmatic system for exploring fundamental physics, which at the same time allows for applications in quantum technologies. The accelerating developments in the field have led to a highly advanced set of engineering techniques that, for example, can tune interactions, shape the external geometry, select among a large set of atomic species with different properties, or control the number of atoms. In particular, it is possible to operate in lower dimensions and drive atomic systems into the strongly correlated regime. In this review, we discuss recent advances in few-body cold atom systems confined in low dimensions from a theoretical viewpoint. We mainly focus on bosonic systems in one dimension and provide an introduction to the static properties before we review the state-of-the-art research into quantum dynamical processes stimulated by the presence of correlations. Besides discussing the fundamental physical phenomena arising in these systems, we also provide an overview of the calculational and numerical tools and methods that are commonly used, thus delivering a balanced and comprehensive overview of the field. We conclude by giving an outlook on possible future directions that are interesting to explore in these correlated systems. [ABSTRACT FROM AUTHOR]

Polypropylene (PP) is a thermoplastic resin widely used in various industrial applications. However, the flammability of PP is a severe drawback that lowers operational safety. This study demonstrates the development of flame‐retardant PP. The co‐adding with various solid acids and a hindered N‐alkoxy amine (NOR116 – Flamestab® NOR 116 FF) affects the combustion behavior of PP in a vertical flame test. The co‐adding of silica alumina (SA) and NOR116 with PP promoted the melt drip, suppressed upward combustion heat, and shorter the combustion time. The decomposition products of NOR116 induced the cleavage of the main chain of PP, and it quenched the radicals on the surface of the SA particles because SA has abundant acidic sites and large pores, facilitating the adsorption of a substantial quantity of NOR116. The molecular weight of PP was controlled to 103 ~ 104 before the combustion to achieve an increase in the melt flow ability and suppress the upward combustion. Furthermore, a small amount of a halogen‐based flame retardant was incorporated into the PP/SA/NOR116 sample, and the specimens could instantly self‐extinguish on the gas phase by radical trap. [ABSTRACT FROM AUTHOR]

In the mean-field approximation, the well-known effect of the critical quantum collapse in a 3D gas of particles pulled to the center by potential U (r) = − U 0 / 2 r 2 is suppressed by repulsive inter-particle interactions, which create the otherwise non-existing s-wave ground state. Here, we address excited bound states carrying angular momentum, with the orbital and magnetic quantum numbers l and m. They exist above a threshold value of the potential's strength, U 0 > l (l + 1) . The sectoral, tesseral, and zonal modes, which correspond to m = l , 0 < m < l , and m = 0 , respectively, are found in an approximate analytical form for relatively small values of U 0 − l (l + 1) . Explicit results are produced for the p- and d-wave states, with l = 1 and 2, respectively. In the general form, the bound states are obtained numerically, confirming the accuracy of the analytical approximation. [ABSTRACT FROM AUTHOR]

We consider a heavy external object moving in an ideal gas of light particles. Collisions with the gas particles transfer momentum to the object, leading to a force that is proportional to the object's velocity but in the opposite direction. In an ideal classical gas at temperature T, the force acting on the object is proportional to T . Quantum statistics causes a deviation from the T -dependence and shows that the force scales with T2 at low temperatures. At T = 0, the force vanishes in a Bose gas but is finite in a Fermi gas. [ABSTRACT FROM AUTHOR]

Quantum optical theory of absorption properties of interacting atoms is developed. The concept of local absorptance is introduced as a derivative of the logarithm of intensity with respect to the distance in the vicinity of a given spatial point and a moment of time. The intensity is represented by the quantum and statistically averaged normal product of creation and annihilation operators of the electromagnetic field. The development of an analytical method of the estimation for the kinetic and optical parameters for the system is proposed here. The calculation method of the absorption coefficient includes thermal atomic motion, Doppler effect, and the short-range interaction between atoms. The absorption coefficient explicitly takes into account the quantum nature of the optical field. The ability of the system to absorb or emit quanta is quantitatively expressed through the special form of interaction integrals. The specific form of integrals results from the structure of the quantum brackets. The interplay between the collective (virtual photon exchange) and binary (optically induced inter-particle bonding) processes determines the system behavior. The spectral profile of the local absorption coefficient for different atomic densities and time intervals is simulated for realistic parameters. [ABSTRACT FROM AUTHOR]

For the first time, the terahertz transmittance spectra of l-alanine have been measured using a single crystal. Measurements were obtained over a large temperature range (12–300 K) and revealed 18 absorptions between 20 and 250 cm−1. These modes were sharp and symmetric, a feature of single crystals and low temperatures. The spectra were directly compared to those of a powdered pellet sample. Raman spectroscopy and x-ray diffraction were used to confirm the sample's structure and purity. With increasing temperature, all modes exhibit spectral redshift, well described by a Bose–Einstein model, indicating the phonon origin of the absorptions. The exceptions are the 91 and 128 cm−1 modes. The former blueshifts. The latter initially blueshifts but transitions to redshifting. Both behaviors are anomalous. Density-functional theory modeling helped assign all the observed modes. [ABSTRACT FROM AUTHOR]

The understanding of nonequilibrium dynamics in many-body quantum systems is a fundamental issue in statistical physics. Experiments that probe universal properties of these systems can address such foundational questions. In this study, we report the measurement of universal dynamics triggered by a quench from the superfluid to normal phase across the Berezinskii-Kosterlitz-Thouless transition in a two-dimensional (2D) Bose gas. We reduced the density by splitting the 2D gas in two, realizing a quench across the critical point. The subsequent relaxation dynamics were probed with matter-wave interferometry to measure the local phase fluctuations. We show that the time evolution of both the phase correlation function and vortex density obeys universal scaling laws. This conclusion is supported by classical-field simulations and interpreted by means of real-time renormalization group theory. [ABSTRACT FROM AUTHOR]

This article reviews the recent developments in the theory of generalised hydrodynamics (GHD) with emphasis on the repulsive one-dimensional Bose gas. We discuss the implications of GHD on the mechanisms of thermalisation in integrable quantum many-body systems as well as its ability to describe far-from-equilibrium behaviour of integrable and near-integrable systems in a variety of quantum quench scenarios. We outline the experimental tests of GHD in cold-atom gases and its benchmarks with other microscopic theoretical approaches. Finally, we offer some perspectives on the future direction of the development of GHD. [ABSTRACT FROM AUTHOR]

The quasi-two-dimensional exciton subsystem in CdSe nanoplatelets is considered. It is theoretically shown that Bose–Einstein condensation (BEC) of excitons is possible at a nonzero temperature in the approximation of an ideal Bose gas and in the presence of an "energy gap" between the ground and the first excited states of the two-dimensional exciton center of inertia of the translational motion. The condensation temperature ( T c ) increases with the width of the "gap" between the ground and the first excited levels of size quantization. It is shown that when the screening effect of free electrons and holes on bound excitons is considered, the BEC temperature of the exciton subsystem increases as compared to the case where this effect is absent. The energy spectrum of the exciton condensate in a CdSe nanoplate is calculated within the framework of the weakly nonideal Bose gas approximation, considering the specifics of two-dimensional Born scattering. [ABSTRACT FROM AUTHOR]

We designed a 3D geometrical model of a metal-oxide gas sensor and its custom packaging and used it in finite element modeling (FEM) analysis for obtaining temperature and heat flux distribution. The 3D computer simulation, performed with GetDP software (version 3.5.0, 13 May 2022), accurately predicted the temperature distribution variation across the entire assembly. Knowing the temperature variation and the location of the hot spots allowed us to select the best electrical interconnect method and to choose the optimal materials combination and optimal geometry. The thermal modeling also confirmed the need to use a low thermal conductivity material to insulate the MOX sensor since the latter is heated to its operational temperature of 250 °C. For that purpose, we used the in-house formulated xerogel–epoxy composite of thermal conductivity of 0.108 W m−1 K−1, which is at least 30% less compared to the best-in-class among commercially available materials. Based on the 3D FEM outputs, we designed, assembled, and characterized a fully functional packaged MOX gas sensor in several configurations. We measured the temperature distribution on all parts of the MOX gas sensor assembly using a thermal imaging infrared (IR) microscope. The results of 3D FEM are in good agreement with the temperature distribution obtained by the non-contact IR thermal characterization. [ABSTRACT FROM AUTHOR]

The thermodynamic properties of the interacting particle–antiparticle boson system at high temperatures and densities were investigated within the framework of scalar and thermodynamic mean-field models. We assume isospin (charge) density conservation in the system. The equations of state and thermodynamic functions are determined after solving the self-consistent equations. We study the relationship between attractive and repulsive forces in the system and the influence of these interactions on the thermodynamic properties of the bosonic system, especially on the development of the Bose–Einstein condensate. It is shown that under "weak" attraction, the boson system has a phase transition of the second order, which occurs every time the dependence of the particle density crosses the critical curve or even touches it. It was found that with a "strong" attractive interaction, the system forms a Bose condensate during a phase transition of the first order, and, despite the finite value of the isospin density, these condensate states are characterized by a zero chemical potential. That is, such condensate states cannot be described by the grand canonical ensemble since the chemical potential is involved in the conditions of condensate formation, so it cannot be a free variable when the system is in the condensate phase. [ABSTRACT FROM AUTHOR]

This review presents the results of observations of high-mass and low-mass X-ray binaries carried out at the Caucasus Mountain Observatory of SAI MSU over the past five years. Interpretation of these observations within the framework of complex unconventional models has led to a number of interesting results. In particular, on the basis of the secular evolutionary increase in the orbital period of the microquasar SS 433 that we discovered, we managed to prove that the relativistic object here is a black hole, and the SS 433 system itself evolves as a semi-detached system due to the fact that the distance between its components increases with time, which prevents the formation of a common envelope. In the microquasar Cyg X-3, an anomalous behavior of IR color indices with the phase of the orbital period was detected. Modeling is carried out and estimates of the parameters of this system are given. In low-mass X-ray binaries (X-ray novae), black hole masses are estimated, spectra of advection-dominated disks are constructed, and an observational justification is given for modern results of three-dimensional gas-dynamic calculations for interacting binaries. [ABSTRACT FROM AUTHOR]

There is a long-standing question of whether it is possible to extend the formalism of equilibrium thermodynamics to the case of nonequilibrium systems in steady-states. We have made such an extension for an ideal gas in a heat flow. Here, we investigated whether such a description exists for the system with interactions: the van der Waals gas in a heat flow. We introduced a steady-state fundamental relation and the parameters of state, each associated with a single way of changing energy. The first law of nonequilibrium thermodynamics follows from these parameters. The internal energy U for the nonequilibrium states has the same form as in equilibrium thermodynamics. For the van der Waals gas, U (S * , V , N , a * , b *) is a function of only five parameters of state (irrespective of the number of parameters characterizing the boundary conditions): the effective entropy S * , volume V, number of particles N, and rescaled van der Waals parameters a * , b * . The state parameters, a * , b * , together with S * , determine the net heat exchange with the environment. The net heat differential does not have an integrating factor. As in equilibrium thermodynamics, the steady-state fundamental equation also leads to the thermodynamic Maxwell relations for measurable steady-state properties. [ABSTRACT FROM AUTHOR]

We study ground states of attractive Bose gases, which are confined in a harmonic trap V (x) = x 1 2 + Λ x 2 2 ( Λ ≥ 1 ) rotating at the velocity Ω . For any 0 ≤ Ω < Ω ∗ : = 2 , where Ω ∗ is called a critical rotational velocity, it is well known that ground states exist if and only if a < a ∗ for some critical constant 0 < a ∗ < ∞ , where a > 0 denotes the product for the number of particles times the absolute value of the scattering length. In this paper, we consider the critical rotating case, where the rotational velocity Ω = Ω ∗ , to study the existence and non-existence of ground states with respect to a > 0 . As imposed in Remark 2.2 of Lewin et al. (Blow-up profile of rotating 2D focusing bose gases. macroscopic limits of quantum systems, Springer, Berlin, 2018), we also analyze the limiting behavior of ground states as a ↗ a ∗ for the case where Ω = Ω a : = Ω ∗ 1 - C 0 (a ∗ - a) m ↗ Ω ∗ , 0 ≤ m < 1 2 and 0 < C 0 < 1 . [ABSTRACT FROM AUTHOR]

The model of a ring threaded by the Aharonov-Bohm flux underlies our understanding of a coupling between gauge potentials and matter. The typical formulation of the model is based upon a single particle picture, and should be extended when interactions with other particles become relevant. Here, we illustrate such an extension for a particle in an Aharonov-Bohm ring subject to interactions with a weakly interacting Bose gas. We show that the ground state of the system can be described using the Bose-polaron concept—a particle dressed by interactions with a bosonic environment. We connect the energy spectrum to the effective mass of the polaron, and demonstrate how to change currents in the system by tuning boson-particle interactions. Our results suggest the Aharonov-Bohm ring as a platform for studying coherence and few- to many-body crossover of quasi-particles that arise from an impurity immersed in a medium. Aharonov-Bohm ring is an intuitive single-particle model applied across many fields of physics, but at the cost of neglecting the many-body interactions between particles and with the environment. Motivated by recent cold-atom experiments on Bose polarons, the authors study a particle contained in Aharonov-Bohm ring and weakly interacting Bose gas. [ABSTRACT FROM AUTHOR]

We consider an inhomogeneous system of N bosons in R 3 confined by an external potential and interacting via a repulsive potential of the form N 2 V (N (x − y)). We prove that the low-energy excitation spectrum of the system is determined by the eigenvalues of an effective one-particle operator, which agrees with Bogoliubov's approximation. [ABSTRACT FROM AUTHOR]

We prove existence results for a system of partial differential equations describing the approximate condensate wavefunction and pair-excitation kernel of a dilute T = 0 Bose gas in the stationary setting, in the presence of a trapping potential and repulsive pairwise atomic interactions. Notably, the Hartree-type equation for the condensate in this system contains contributions from non-condensate particles, and the pair excitation kernel satisfies a nonlinear operator equation. The techniques employed include a direct variational principle and also an iterative procedure for constructing solutions. [ABSTRACT FROM AUTHOR]

We consider a system of N bosons, in the two-dimensional unit torus. We assume particles to interact through a repulsive two-body potential, with a scattering length that is exponentially small in N (Gross–Pitaevskii regime). In this setting, we establish the validity of the predictions of Bogoliubov theory, determining the ground state energy of the Hamilton operator and its low-energy excitation spectrum, up to errors that vanish in the limit N → ∞ . [ABSTRACT FROM AUTHOR]

The notion of a crosscap state, a special conformal boundary state first defined in 2d CFT, was recently generalized to 2d massive integrable quantum field theories and integrable spin chains. It has been shown that the crosscap states preserve integrability. In this work, we first generalize this notion to the Lieb-Liniger model, which is a prototype of integrable non-relativistic many-body systems. We then show that the defined crosscap state preserves integrability. We derive the exact overlap formula of the crosscap state and the on-shell Bethe states. As a byproduct, we prove the conjectured overlap formula for integrable spin chains rigorously by coordinate Bethe ansatz. It turns out that the overlap formula for both models take the same form as a ratio of Gaudin-like determinants with a trivial prefactor. Finally we study quench dynamics of the crosscap state, which turns out to be surprisingly simple. The stationary density distribution is simply a constant. We also derive the analytic formula for dynamical correlation functions in the Tonks-Girardeau limit. [ABSTRACT FROM AUTHOR]

In the present paper, we investigate the ground state of Tonks–Girardeau gas under density-dependent gauge potential. With Bose–Fermi mapping method, we obtain the exact ground-state wavefunction for the system confined in a harmonic potential. Based on the ground-state wavefunction, the reduced one-body density matrix (ROBDM), natural orbitals and their occupations, and the momentum distributions are obtained. Compared with the case without gauge potential, the present wavefunction and ROBDM have additional phase factors induced by gauge potential. The momentum distribution is the convolution of that without gauge potential to the Fourier transformation of definite integral of gauge potential. It is shown that because of the density-dependent gauge potential, the peak of momentum distributions deviates from zero momentum and the Bose gas takes finite total momentum. In particular, the momentum distribution is no longer symmetric although the total momentum can become zero by adding a constant to the gauge potential. [ABSTRACT FROM AUTHOR]

The morphological, transport, and terahertz optical properties of DC magnetron-sputtered granular molybdenum thin films with nano-grains embedded in an amorphous molybdenum/molybdenum oxide matrix have been studied in their normal and superconducting states. The superconducting transition temperatures of these films are much higher than that of bulk molybdenum. The optical properties of these thin films have been studied using terahertz time-domain spectroscopy. Their properties have been compared with those of the existing materials used for the development of radiation detectors. The films' resistivity lies in the >100 μΩ cm range, ideal for making highly sensitive radiation detectors. Hall measurements indicate holes as the dominant carriers with very small mean free path and mobility. In the normal state, the films are disordered bad metals. However, they have a large superfluid density and stiffness in their superconducting state. The properties of the films in the normal and superconducting states are promising for their use in cryogenic radiation detectors for microwave, terahertz, and far-infrared frequency ranges. [ABSTRACT FROM AUTHOR]

We investigate the dynamics of the hard-core Bose gas in a harmonic trap with a periodic drive. With Bose–Fermi mapping method, the time-dependent wavefunction can be constructed based on the solution of single-particle Schrödinger equation under the periodic drive. It is shown that both the density distribution and momentum distribution preserve their initial profiles during the time evolution and behave as if the hard-core Bose gas is an entity particle. When the frequency of driving force is close to the trap frequency of harmonic potential, both the density distribution and momentum distribution exhibit the behaviors of classical beats, which is similar to the behavior of the composition of two classical harmonic oscillators with similar frequencies. [ABSTRACT FROM AUTHOR]

A theoretical analysis of the rotational dynamics induced by off-axis binary collisions of quantum droplets constituted by ultracold atoms is reported. We focus on quantum droplets formed by degenerate dilute Bose gases made from binary mixtures of alkaline atoms under feasible experimental conditions. The stability of the ground state is known to be longer for the chosen heteronuclear gases than for the homonuclear ones. In both cases, we find that the dynamics seem to privilege high similarity of the density of each atomic species. However, the evolution of the phase of the corresponding order parameter differs significantly for heteronuclear admixtures. We evaluate the fidelity as a figure of merit for the overlap between the order parameters of each atomic species. Dynamical evidence of the differences between the phases of the order parameters is predicted to manifest in their corresponding linear and angular momenta. We numerically verify that the total angular and linear momenta are both conserved during the collision. Some direct correlations between the Weber number and the impact parameter with the distribution of the dynamical variables are established. [ABSTRACT FROM AUTHOR]

We consider a general system of interacting random loops which includes several models of interest, such as the Spin O(N) model,random lattice permutations, a version of the interacting Bose gas in discrete space and of the loop O(N) model. We consider the system in Z d , d ≥ 3 , and prove the occurrence of macroscopic loops whose length is proportional to the volume of the system. More precisely, we approximate Z d by finite boxes and, given any two vertices whose distance is proportional to the diameter of the box, we prove that the probability of observing a loop visiting both is uniformly positive. Our results hold under general assumptions on the interaction potential, which may have bounded or unbounded support or introduce hard-core constraints. [ABSTRACT FROM AUTHOR]

We show that all the Bose–Einstein (BE) condensations of Bose and Fermi systems can be formulated using the common 'boson' operator (valid below the BE condensation temperature T c ) with the coherent translational momentum q = 0 (center-of-mass momentum in fermion system). The BE condensation is identified as the condensate of hopping bosons in Bose system and hopping fermion-pairs in Fermi system and the condensation energy is given by those average hopping energy times their condensate. We demonstrate that this scheme is actually working in all the BE condensations of strong-coupling fermion-pair system, weak-coupling Cooper-pair BCS system and the ideal Bose gas system. We find that the change of cuprate high- T c superconductivity from the underdoped to the overdoped regime is the doping-induced crossover from strong- to weak-coupling BE condensation arising from the same origin of the attractive superexchange interaction. We also study the BE condensation in the large attractive - U Hubbard model and obtain a new BE-condensed ground state which is different from the one considered hitherto. We briefly comment on the more recently discovered BE condensations and their crossovers in the ultra-cold alkaline Fermi atom gases. [ABSTRACT FROM AUTHOR]

We study Bose gases in $d \ge 2$ dimensions with short-range repulsive pair interactions at positive temperature, in the canonical ensemble and in the thermodynamic limit. We assume the presence of hard Poissonian obstacles and focus on the non-percolation regime. For sufficiently strong interparticle interactions, we show that almost surely there cannot be Bose–Einstein condensation into a sufficiently localized, normalized one-particle state. The results apply to the canonical eigenstates of the underlying one-particle Hamiltonian. [ABSTRACT FROM AUTHOR]

Heat-transfer deterioration is a thermal phenomenon existing one or multiple wall temperature fluctuation along the flowing direction on porous heat-transfer surface. Effects of condensate film on deterioration phenomenon for non-condensation heat-transfer process has been reported in the literature, but for condensation process is seldom proposed and specifically researched. Here, the condensation heat and mass-transfer characteristics on micro-porous ceramic membrane module is investigated experimentally and numerically, with absolute humidity of artificial flue gas, inlet temperature of cooling water, volume flux of cooling water covered the ranges of 0.6375 – 0. 6845 kg/m3, 294.4 –2 97.2 K , 0.32 – 0. 41 m3/s, respectively. Sudden temperature fluctuation and collapsing water-recovery efficiency are observed nearby 1/3 region of the ceramic membrane module, which corresponds to the fact that remaining condensate film induces large thermal resistance because of the low thermal conductivity of the gas-like phase, and causes fluctuation of temperature gradient (i.e. condensation heat-transfer deterioration) on membrane surface. It is found that, condensation-regime transition range decreases to 0.763 – 0.781 at 1/3 region of membrane module, which results in a more remarkable permeation hysteresis effect and a more dominant capillary condensation process. The present findings of this paper are helpful to optimize the design parameters and operation conditions of micro-porous ceramic membrane modules. • Condensation performance on local regions was researched by experiment and CFD. • Sudden temperature fluctuation and collapsing efficiency were investigated. • Condensation heat-transfer deterioration parameter on porous media was proposed. • Relationship between momentum force and capillary force was investigated. [ABSTRACT FROM AUTHOR]