Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCollective oscillations of dipolar Bose-Einstein condensates and accurate comparison between contact and dipolar interaction
134
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We propose a scheme for the measurement of the s-wave scattering length $a$ of an atom or molecule with significant dipole-dipole interaction with an accuracy at the percent level. The frequencies of the collective oscillations of a Bose-Einstein condensate are shifted by the magnetic dipole interaction. The shift is polarization dependent and proportional to the ratio $epsilon_{dd}$ of dipolar and s-wave coupling constants. Measuring the differences in the frequencies for different polarization we can extract the value of $epsilon_{dd}$ and thus measure $a$. We calculate the frequency shifts for a large variety of non-axisymmetric harmonic traps in the Thomas-Fermi limit and find optimal trapping geometries to maximize the shifts.
rate research
Read More
We have measured the relative strength $epsilon_dd$ of the magnetic dipole-dipole interaction compared to the contact interaction in a chromium Bose-Einstein condensate. We analyze the asymptotic velocities of expansion of a dipolar chromium BEC with different orientations of the atomic magnetic dipole moments. By comparing them with numerical solutions of the hydrodynamic equations for dipolar condensates, we are able to determine $epsilon_dd = 0.159pm0.034$ with high accuracy. Since the absolute strength of the dipole-dipole interaction is known exactly, the relative strength of the dipoledipole interaction can be used to determine the s-wave scattering length $a = 5.08pm1.06cdot10^-9 m = 96pm20 a0$ of 52Cr. This is fully consistent with our previous measurements on the basis of Feshbach resonances.
We investigate the time taken for global collapse by a dipolar Bose-Einstein condensate. Two semi-analytical approaches and exact numerical integration of the mean-field dynamics are considered. The semi-analytical approaches are based on a Gaussian ansatz and a Thomas-Fermi solution for the shape of the condensate. The regimes of validity for these two approaches are determined, and their predictions for the collapse time revealed and compared with numerical simulations. The dipolar interactions introduce anisotropy into the collapse dynamics and predominantly lead to collapse in the plane perpendicular to the axis of polarization.
Magnetic dipole-dipole interaction dominated Bose-Einstein condensates are discussed under spinful situations. We treat the spin degrees of freedom as a classical spin vector, approaching from large spin limit to obtain an effective minimal Hamiltonian; a version extended from a non-linear sigma model. By solving the Gross-Pitaevskii equation we find several novel spin textures where the mass density and spin density are strongly coupled, depending upon trap geometries due to the long-range and anisotropic natures of the dipole-dipole interaction.
We perform a full three-dimensional study on miscible-immiscible conditions for coupled dipolar and non-dipolar Bose-Einstein condensates (BEC), confined within anisotropic traps. Without loosing general miscibility aspects that can occur for two-component mixtures, our main focus was on the atomic erbium-dysprosium ($^{168}$Er-$^{164}$Dy) and dysprosium-dysprosium ($^{164}$Dy-$^{162}$Dy) mixtures. Our analysis for pure-dipolar BEC was limited to coupled systems confined in pancake-type traps, after considering a study on the stability regime of such systems. In case of non-dipolar systems with repulsive contact intneeractions we are able to extend the miscibility analysis to coupled systems with cigar-type symmetries. For a coupled condensate with repulsive inter- and intra-species two-body interactions, confined by an external harmonic trap, the transition from a miscible to an immiscible phase is verified to be much softer than in the case the system is confined by a symmetric hard-wall potential. Our results, presented by density plots, are pointing out the main role of the trap symmetry and inter-species interaction for the miscibility. A relevant parameter to measure the overlap between the two densities was defined and found appropriate to quantify the miscibility of a coupled system.
The partially attractive character of the dipole-dipole interaction leads to phonon instability in dipolar condensates, which is followed by collapse in three-dimensional geometries. We show that the nature of this instability is fundamentally different in two-dimensional condensates, due to the dipole-induced stabilization of two-dimensional bright solitons. As a consequence, a transient gas of attractive solitons is formed, and collapse may be avoided. In the presence of an harmonic confinement, the instability leads to transient pattern formation followed by the creation of stable two-dimensional solitons. This dynamics should be observable in on-going experiments, allowing for the creation of stable two-dimensional solitons for the first time ever in quantum gases.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
