Structure factor for a Bose fluid

The structure factor is calculated for a Bose fluid using an expression for S(k), which is approximately valid for all values of k. Marked fluctuations appear for $\text{k = 2.15}\text{A}\text{?}{}^{-1}$, near the roton dip in E_k, and at $\text{k = 3.65}\text{A}\text{?}{}^{-1}$ near the dip in the second branch of E_k. Our calculations are indirectly a theoretical justification for the existence of a second branch in E_k. The results presented here agree fairly well with the experimental values for $\text{k >; 3.0}\text{A}\text{?}{}^{-1}$ along with a dip at $\text{k = 3.67}\text{A}\text{?}{}^{-1}$ which has not been reported earlier. It also suggests the existence of two waves, phonons and rotons, for $\text{k >; 3.0}\text{A}\text{?}{}^{-1}$.     

Interacting excitations in a Bose fluid

Within the Bogoliubov-Zubarev formalism we develop a graphical perturbation theory of a Bose fluid for finite temperatures. We derive the quasiparticle lifetime and a Boltzmann equation for excitations, restricting ourselves to lowest order perturbation theory. All results are expressed in terms of the parameter ², occuring in the Bogoliubov-Zubarev formalism, which in lowest order is equal to the liquid structure factor at zero temperature.     

Quantum backreaction of quantum fluid in Bose Einstein condensates

In this paper, with the full field operator \hat ψ expressed in terms of a particle-number-conserving mean-field ansatz, we investigate the dynamical behaviour of Bose--Einstein condensates from microscopic physics. Including the first-order term correction from single-particle excitation and the remaining higher-order term correction from collective excitations simultaneously, we obtain the formulation for a closed local expression of quantum backreaction Q, and discuss the influence on static Bose--Einstein condensates. Even though the quantum backreaction is small, it still has some influence on its dynamics.     

双参数变形多模玻色算符的代数结构及其应用(Ⅰ)

构造了两个满足量子Heisenberg-Weyl代数的双参数变形多模玻色算符,研究了它们的代数结构,作为应用,给出了双参数变形多模量子群SU(2)_q,s和SU/(1,1)_q,s的Holstein-Primakoff实现,并分别构造了这两个玻色算符二次幂的本征态,证明了它们的完备性.     

Self-Bound Quantum Droplet with Internal Stripe Structure in One-Dimensional Spin-Orbit-Coupled Bose Gas

We study the quantum-droplet state in a three-dimensional(3D) Bose gas in the presence of 1D spin-orbit coupling and Raman coupling, especially the stripe phase with density modulation, by numerically computing the ground state energy including the mean-field energy and Lee–Huang–Yang correction. In this droplet state,the stripe can exist in a wider range of Raman coupling, compared with the BEC-gas state. More intriguingly,both spin-orbit coupling and Raman coupling strengths can be used to tune the droplet density.     

Structure of the square-shoulder fluid

The structural properties of square-shoulder fluids are derived from the use of the rational function approximation method. The computation of both the radial distribution function and the static structure factor involves mostly analytical steps, requiring only the numerical solution of a single transcendental equation. The comparison with available simulation data and with numerical solutions of the Percus–Yevick and hypernetted-chain integral equations shows that the present approximation represents an improvement over the Percus–Yevick theory for this system and a reasonable compromise between accuracy and simplicity.     

Dynamical structure factor and spin-density separation for a weakly interacting two-component Bose gas

We show that spin-density separation in a Bose gas is not restricted to 1D but also occurs in higher dimensions. The ratio (alpha) of the intraspecies atom-atom interaction strength to the interspecies interaction strength strongly influences the dynamics of spin-density separation and the elementary excitations. The density wave is phononlike for all values of alpha. For alpha < 1, the spin wave is also phononlike. The spin waves have a quadratic dispersion in the alpha=1 coupling regime, while in the phase separated regime (alpha > 1) the spin waves are found to be damped. The dynamical structure factor reveals two distinct peaks corresponding to the density and spin waves for alpha < or =1. For alpha > 1 there is only one dynamical structure factor peak corresponding to the density wave.     

Cold Bose stars

By solving the Einstein equations coupled to a noninteracting quantum Bose field we determine the mass, density, and radius of equilibrium states of cold Bose matter localized under its own gravity. In particular we find that the maximum mass of a cold Bose star is 0.633/Gm.     

双参数变形多模玻色算符的代数结构及其应用(Ⅱ)

给出了双参数变形量子代数ＳＵ（２）ｑ，ｓ和ＳＵ（１，１）ｑ，ｓ的多模Ｊｏｒｄａｎ－Ｓｃｈｗｉｎｇｅｒ实现。     

Bounded Bose Fields

Examples for bounded Bose fields in two dimensions are presented.     

玻色气体的磁性

物质磁性一直是凝聚态物理研究的重要课题.以往对磁性的探索主要是以费米子（局域或巡游的电子）为研究对象.由于传统的玻色系统液氦没有自旋,不表现磁性,玻色系统的磁性很少被关注.碱金属原子气体玻色-爱因斯坦凝聚的实现,在开辟了冷原子物理研究领域的同时,也打开了研究玻色系统磁性的大门.这是因为碱金属原子通常具有超精细结构,是旋量玻色气体,能够展示磁性.文章通过对比费米气体的相关结果,介绍了旋量玻色气体磁性的研究概况和最新进展,特别是铁磁性玻色气体的磁性相变以及在低温下铁磁性凝聚体的动力学特征.     

玻色气体的磁性

物质磁性一直是凝聚态物理研究的重要课题.以往对磁性的探索主要是以费米子(局域或巡游的电子)为研究对象.由于传统的玻色系统液氦没有自旋,不表现磁性,玻色系统的磁性很少被关注.碱金属原子气体玻色-爱因斯坦凝聚的实现,在开辟了冷原子物理研究领域的同时,也打开了研究玻色系统磁性的大门.这是因为碱金属原子通常具有超精细结构,是旋量玻色气体,能够展示磁性.文章通过对比费米气体的相关结果,介绍了旋量玻色气体磁性的研究概况和最新进展,特别是铁磁性玻色气体的磁性相变以及在低温下铁磁性凝聚体的动力学特征.     

Dilute Bose gas revised

The well-known results concerning a dilute Bose gas with the short-range repulsive interaction should be reconsidered due to a thermodynamic inconsistency of the method being basic to much of the present understanding of this subject. The aim of our paper is to propose another way of treating the dilute Bose gas with an arbitrary strong interaction. Using the reduced density matrix of the second order and a variational procedure, this way allows us to escape the inconsistency mentioned and operate with singular potentials of the Lennard-Jones type. The derived expansion of the condensate depletion in powers of the boson density n=N/V reproduces the familiar result, while the expansion for the mean energy per particle is of the form epsilon=2 pi planck(2)an/m[1+128/(15 square root of [pi]) square root of [na(3)](1-5b/8a)+...], where a is the scattering length and b> or =0 stands for one more characteristic length depending on the shape of the interaction potential (in particular, for the hard spheres a=b). All the consideration concerns the zero temperature.     

Bose condensation in biosystems

A microscopic approach to Fröhlich's theory of Bose condensation in biological systems is discussed. The conclusions from this microscopic analysis offer further support for Fröhlich's hypothesis.     

On the relation between the normal fluid density and the one particle Green function for Bose fluids

The normal fluid density is defined through the moment of inertia of a cylinder rotating about its axis, in the limit of infinitesimal angular velocity. The angular momentum may be calculated from the one particle Green function, and this leads to the relation between ?_n and the Green function.We then consider an ensemble in which the fluid is constrained to irrotational flow. For statistical states which are “locally gauge invariant” we show that ρ_n, as defined previously, is identical to the full density. This demonstrates the connection between superfluidity and the breaking of local gauge symmetry.Finally, we apply the result to the gas of non-interacting quasi-particles and the fully interacting Bose fluid in the limit of very low temperatures. In both cases we reproduce the Landau expression for ρ_n in terms of the quasiparticle occupation numbers, and derive the well-known result for real superfluid helium that ρ_n ～ T⁴ as T→0.     

Relativistic charged Bose gas

The excitation spectrum of a relativistic spin-zero charged Bose gas is obtained in a dielectric response formulation. Relativity introduces a dip in the spectrum and the consequences of this dip for the thermodynamic functions are discussed.