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Register a new userTemperature Dependence of Damping and Frequency Shifts of the Scissors Mode of a trapped Bose-Einstein Condensate
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We have studied the properties of the scissors mode of a trapped Bose-Einstein condensate of $^{87}$Rb atoms at finite temperature. We measured a significant shift in the frequency of the mode below the hydrodynamic limit and a strong dependence of the damping rate as the temperature increased. We compared our damping rate results to recent theoretical calculations for other observed collective modes finding a fair agreement. From the frequency measurements we deduce the moment of inertia of the gas and show that it is quenched below the transition point, because of the superfluid nature of the condensed gas.
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A scissors mode of a rotating Bose-Einstein condensate is investigated both theoretically and experimentally. The condensate is confined in an axi-symmetric harmonic trap, superimposed with a small rotating deformation. For angular velocities larger than $omega_perp/sqrt2 $, where $omega_perp$ is the radial trap frequency, the frequency of the scissors mode is predicted to vanish like the square root of the deformation, due to the tendency of the system to exhibit spontaneous rotational symmetry breaking. Measurements of the frequency confirm the predictions of theory. Accompanying characteristic oscillations of the internal shape of the condensate are also calculated and observed experimentally.
We derive the exact density profile of a harmonically trapped Bose-Einstein condensate (BEC) which has dipole-dipole interactions as well as the usual s-wave contact interaction, in the Thomas-Fermi limit. Remarkably, despite the non-local anisotropic nature of the dipolar interaction, the density turns out to be an inverted parabola, just as in the pure s-wave case, but with a modified aspect ratio. The ``scaling solution approach of Kagan, Surkov, and Shlyapnikov [Phys. Rev. A 54, 1753 (1996)] and Castin and Dum [Phys. Rev. Lett. 77}, 5315 (1996)] for a BEC in a time-dependent trap can therefore be applied to a dipolar BEC, and we use it to obtain the exact monopole and quadrupole shape oscillation frequencies.
Surface modes in a Bose-Einstein condensate of sodium atoms have been studied. We observed excitations of standing and rotating quadrupolar and octopolar modes. The modes were excited with high spatial and temporal resolution using the optical dipole force of a rapidly scanning laser beam. This novel technique is very flexible and should be useful for the study of rotating Bose-Einstein condensates and vortices.
We study the dynamics of an impurity embedded in a trapped Bose-Einstein condensate (Bose polaron), by recalling the quantum Brownian motion model. It is crucial that the model considers a parabolic trapping potential to resemble the experimental conditions. Thus, we detail here how the formal derivation changes due to the gas trap, in comparison to the homogeneous gas. We first find that the presence of a gas trap leads to a new form of the bath-impurity coupling constant and a larger degree in the super-ohmicity of the spectral density. This is manifested as a different dependence of the system dynamics on the past history. To quantify this, we introduce several techniques to compare the different amount of memory effects arising in the homogeneous and inhomogeneous gas. We find that it is higher in the second case. Moreover, we calculate the position variance of the impurity, represenitng a measurable quantity. We show that the impurity experiences super-diffusion and genuine position squeezing. Wdetail how both effects can be enhanced or inhibited by tuning the Bose-Einstein condensate trap frequency.
A hydrodynamic description is used to study the zero-temperature properties of a trapped spinor Bose-Einstein condensate in the presence of a uniform magnetic field. We show that, in the case of antiferromagnetic spin-spin interaction, the polar and ferromagnetic configurations of the ground state can coexist in the trap. These two phases are spatially segregated in such a way that the polar state occupies the inner part while the ferromagnetic state occupies the outer part of the atomic cloud. We also derive a set of coupled hydrodynamic equations for the number density and spin density excitations of the system. It is shown that these equations can be analytically solved for the system in an isotropic harmonic trap and a constant magnetic field. Remarkably, the related low lying excitation spectra are completely determined by the solutions in the region occupied by the polar state. We find that, within the Thomas-Fermi approximation, the presence of a constant magnetic field does not change the excitation spectra which still possess the similar form of that obtained by Stringari.
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