Stefano Giovanazzi

Exact Hydrodynamics of a Trapped Dipolar Bose-Einstein Condensate

We present exact results in the Thomas-Fermi regime for the statics and dynamics of a harmonically trapped Bose-Einstein condensate that has dipole-dipole interactions in addition to the usual s-wave contact interactions. Remarkably, despite the nonlocal and anisotropic nature of the dipolar interactions, the density profile in a general time-dependent harmonic trap is an inverted parabola. The evolution of the condensate radii is governed by local, ordinary differential equations, and as an example we calculate the monopole and quadrupole shape oscillation frequencies.

Exact solution of the Thomas-Fermi equation for a trapped Bose-Einstein condensate with dipole-dipole interactions

We derive an exact solution to the Thomas-Fermi equation for a Bose-Einstein condensate (BEC) which has dipole-dipole interactions as well as the usual s-wave contact interaction, in a harmonic trap. Remarkably, despite the nonlocal anisotropic nature of the dipolar interaction the solution is an inverted parabola, as in the pure s-wave case, but with a different aspect ratio. We explain in detail the mathematical tools necessary to describe dipolar BECs with or without cylindrical symmetry. Various properties such as electrostriction and stability are discussed.

Conditions for one-dimensional supersonic flow of quantum gases

One can use transsonic Bose-Einstein condensates of alkali atoms to establish the laboratory analog of the event horizon and to measure the acoustic version of Hawking radiation. We determine the conditions for supersonic flow and the Hawking temperature for realistic condensates on waveguides where an external potential plays the role of a supersonic nozzle. The transition to supersonic speed occurs at the potential maximum and the Hawking temperature is entirely determined by the curvature of the potential.

Instabilities and the roton spectrum of a quasi-1D Bose-Einstein condensed gas with dipole-dipole interactions

Abstract.We point out the possibility of having a roton-type excitation spectrum in a quasi-1D Bose-Einstein condensate with dipole-dipole interactions. Normally such a system is quite unstable due to the attractive portion of the dipolar interaction. However, by reversing the sign of the dipolar interaction using either a rotating magnetic field or a laser with circular polarization, a stable cigar-shaped configuration can be achieved whose spectrum contains a ‘roton’ minimum analogous to that found in helium II. Dipolar gases also offer the exciting prospect of tuning the depth of this ‘roton’ minimum by directly controlling the interparticle interaction strength. When the minimum touches the zero-energy axis the system is once again unstable, possibly to the formation of a density wave.

One-dimensional compression of Bose-Einstein condensates by laser-induced dipole-dipole interactions

We consider a trapped cigar-shaped atomic Bose-Einstein condensate irradiated by a single far-off resonance laser polarized along the cigar axis. The resulting laser-induced dipole-dipole interactions between the atoms significantly change the size of the condensate, and can even cause its self-trapping.

New Regimes in Cold Gases via Laser-Induced Long-Range Interactions

The modification of the properties of a Bose-Einstein or a Fermi-Dirac atomic gas due to laser-induced dipole-dipole interactions between the atoms are considered. Nearly-isotropic illumination of the sample by spectrally-fluctuating laser beams averages out the static r −3 dipole-dipole interaction, leaving the retarded r −1 “selfgravitating” attraction in the near zone. The analogies of ultracold many-atom systems, self-bound by such laser-induced “gravity”, with compact stars (“Bose stars” or “White Dwarfs”) are emphasized. Even a single plane-wave laser induces dipole-dipole interactions capable of causing a cigar-shaped Bose condensate to exhibit self binding and density modulations.

Squeezing in a dipolar Bose—Einstein condensed gas

Abstract We consider a gaseous atomic Bose—Einstein condensate with dipole—dipole interactions induced by a far off-resonance laser. The long-range dipolar interactions introduce atom—atom correlations on the new scale of the laser wavelength, giving a controllable method of squeezing low energy modes. At high enough laser intensities the correlations lead to a roton minimum in the excitation spectrum.

Bose-Einstein Condensates with Laser-Induced Dipole-Dipole Interactions

We consider the interparticle correlations in a gaseous Bose-Einstein condensate which has laser-induced dipole-dipole interactions. These correlations, which are tunable and occur at the length scale of the laser wavelength, can lead to a ‘roton’ minimum in the excitation spectrum.