Hybrid phase-space simulation method for interacting Bose fields

Bose-Einstein Condensation Temperature of Homogenous Weakly Interacting Bose Gas in Variational Perturbation Theory Through Six Loops

We compute the shift of the transition temperature for a homogenous weakly interacting Bose gas in leading order in the scattering length a for given particle density n. Using variational perturbation theory through six loops in a classical three-dimensional scalar field theory, we obtain Delta T_c/T_c = 1.25+/-0.13 a n^(1/3), in agreement with recent Monte-Carlo results.

On quantum time crystals and interacting gauge theories in atomic Bose-Einstein condensates

We study the dynamics of a Bose-Einstein condensate trapped circumferentially on a ring, and which is governed by an interacting gauge theory. We show that the associated density-dependent gauge potential and concomitant current nonlinearity permits a ground state in the form of a rotating chiral bright soliton. This chiral soliton is constrained to move in one direction by virtue of the current nonlinearity, and represents a time crystal in the same vein as Wilczek's original proposal.

Bose-Einstein condensation of two interacting particles

We investigate the notion of Bose-Einstein condensation of interacting particles. The definition of the condensate is based on the existence of the dominant eigenvalue of the single-particle density matrix. The statistical properties and the characteristic temperature are computed exactly in the soluble models of two interacting atoms.

Loschmidt echo in one-dimensional interacting Bose gases

We explore Loschmidt echo in two regimes of one-dimensional (1D) interacting Bose gases: the strongly interacting Tonks-Girardeau (TG) regime, and the weakly-interacting mean-field regime. We find that the Loschmidt echo of a TG gas decays as a Gaussian when small perturbations are added to the Hamiltonian (the exponent is proportional to the number of particles and the magnitude of a small perturbation squared). In the mean-field regime the Loschmidt echo decays faster for larger interparticle interactions (nonlinearity), and it shows richer behavior than the TG Loschmidt echo dynamics, with …

论Kac-Luttinger模型中相互作用玻色气体的玻色-爱因斯坦凝聚

On Bose-Einstein condensation in interacting Bose gases in the Kac-Luttinger model

本文在Kac-Luttinger随机模型中研究零温平均场型相互作用的玻色气体，利用Sznitman关于无相互作用玻色气体谱隙的最新结果，证明了玻色-爱因斯坦凝聚以概率或几乎必然发生并凝聚到Hartree型泛函极小元。

Experimental evidence for the breakdown of a Hartree-Fock approach in a weakly interacting Bose gas

We study the formation of a quasi-condensate in a nearly one dimensional, weakly interacting trapped atomic Bose gas. We show that a Hartree Fock (mean-field) approach fails to explain the presence of the quasi-condensate in the center of the cloud: the quasi-condensate appears through an interaction-driven cross-over and not a saturation of the excited states. Numerical calculations based on Bogoliubov theory give an estimate of the cross-over density in agreement with experimental results.

Time Parametrizations in Long-Range Interacting Bose-Einstein Condensates

Time-reparametrization invariance in general relativistic space-time does not allow us to single out a time in quantum mechanics in a mechanical way of measurement. Motivated by this problem, we examine this gauge invariance in the ground state of the quasi-stationary coarse-grained state of a long-range interacting closed system of identical or identified, macroscopic, and spatiotemporally inhomogeneous Bose-Einstein condensates in the thermodynamic and Newtonian limits. As a result, we find that it is a theoretical counterexample of this gauge invariance, except for proper-time translational…

Bose-Einstein Condensation Temperature of Homogenous Weakly Interacting Bose Gas in Variational Perturbation Theory Through Seven Loops

The shift of the Bose-Einstein condensation temperature for a homogenous weakly interacting Bose gas in leading order in the scattering length `a' is computed for given particle density `n.' Variational perturbation theory is used to resum the corresponding perturbative series for Delta<phi^2>/Nu in a classical three-dimensional scalar field theory with coupling `u' and where the physical case of N=2 field components is generalized to arbitrary N. Our results for N=1,2,4 are in agreement with recent Monte-Carlo simulations; for N=2, we obtain Delta T_c/T_c = 1.27 +/- 0.11 a n^(1/3). We use sev…

Bose polarons in the strongly interacting regime

When an impurity is immersed in a Bose-Einstein condensate, impurity-boson interactions are expected to dress the impurity into a quasiparticle, the Bose polaron. We superimpose an ultracold atomic gas of $^{87}$Rb with a much lower density gas of fermionic $^{40}$K impurities. Through the use of a Feshbach resonance and RF spectroscopy, we characterize the energy, spectral width and lifetime of the resultant polaron on both the attractive and the repulsive branches in the strongly interacting regime. The width of the polaron in the attractive branch is narrow compared to its binding energy, e…

相互作用玻色凝聚气体

Interacting Bose-condensed gases

本文综述了玻色凝聚气体中相互作用的影响，涵盖接触与偶极相互作用，讨论基态修正、临界行为、幺正区、量子液滴及超固体等关键现象。

Two-body momentum correlations in a weakly interacting one-dimensional Bose gas

We analyze the two-body momentum correlation function for a uniform weakly interacting one-dimensional Bose gas. We show that the strong positive correlation between opposite momenta, expected in a Bose-Einstein condensate with a true long-range order, almost vanishes in a phase-fluctuating quasicondensate where the long-range order is destroyed. Using the Luttinger liquid approach, we derive an analytic expression for the momentum correlation function in the quasicondensate regime, showing (i) the reduction and broadening of the opposite-momentum correlations (compared to the singular behavio…

Entanglement spectrum: Identification of the transition from vortex-liquid to vortex-lattice state in a weakly interacting rotating Bose-Einstein condensate

We use entanglement to investigate the transition from vortex liquid phase to vortex lattice phase in weakly interacting rotating Bose-Einstein condensate (BEC). Ground state entanglement spectrum is analyzed to distinguish these two different phases. For the torus geometry, the low-lying part of ground state entanglement spectrum, as well as the behavior of its lowest level change clearly when the transition occurs. For the sphere geometry, the disappearance of entanglement gap in the conformal limit (CL) can indicate this transition. We also show that the decrease of entanglement between par…

Microscopic Evolution of a Weakly Interacting Homogeneous Bose Gas

We provide a detailed description of the nonequilibrium time evolution of an interacting homogeneous Bose-Einstein condensate. We use a nonperturbative in-medium quantum field theory approach as a microscopic model for the Bose gas. The real-time dynamics of the condensate is encoded in a set of self-consistent equations which corresponds to an infinite sum of ladder Feynman diagrams. The crucial role played by the interaction between fluctuations for the instability generation is thoroughly described.