749 research outputs found
Long wavelength spin dynamics of ferromagnetic condensates
We obtain the equations of motion for a ferromagnetic Bose condensate of
arbitrary spin in the long wavelength limit. We find that the magnetization of
the condensate is described by a non-trivial modification of the
Landau-Lifshitz equation, in which the magnetization is advected by the
superfluid velocity. This hydrodynamic description, valid when the condensate
wavefunction varies on scales much longer than either the density or spin
healing lengths, is physically more transparent than the corresponding
time-dependent Gross-Pitaevskii equation. We discuss the conservation laws of
the theory and its application to the analysis of the stability of magnetic
helices and Larmor precession. Precessional instabilities in particular provide
a novel physical signature of dipolar forces. Finally, we discuss the
anisotropic spin wave instability observed in the recent experiment of
Vengalattore et. al. (Phys. Rev. Lett. 100, 170403, (2008)).Comment: arXiv version contains additional Section V relevant to the
experiment of Vengalattore et. al. (Phys. Rev. Lett. 100, 170403, (2008)
Internal Vortex Structure of a Trapped Spinor Bose-Einstein Condensate
The internal vortex structure of a trapped spin-1 Bose-Einstein condensate is
investigated. It is shown that it has a variety of configurations depending on,
in particular, the ratio of the relevant scattering lengths and the total
magnetization.Comment: replacement; minor grammatical corrections but with additional
figure
From multimode to monomode guided atom lasers: an entropic analysis
We have experimentally demonstrated a high level of control of the mode
populations of guided atom lasers (GALs) by showing that the entropy per
particle of an optically GAL, and the one of the trapped Bose Einstein
condensate (BEC) from which it has been produced are the same. The BEC is
prepared in a crossed beam optical dipole trap. We have achieved isentropic
outcoupling for both magnetic and optical schemes. We can prepare GAL in a
nearly pure monomode regime (85 % in the ground state). Furthermore, optical
outcoupling enables the production of spinor guided atom lasers and opens the
possibility to tailor their polarization
Anisotropic excitation spectrum of a dipolar quantum Bose gas
We measure the excitation spectrum of a dipolar Chromium Bose Einstein
Condensate with Raman-Bragg spectroscopy. The energy spectrum depends on the
orientation of the dipoles with respect to the excitation momentum,
demonstrating an anisotropy which originates from the dipole-dipole
interactions between the atoms. We compare our results with the Bogoliubov
theory based on the local density approximation, and, at large excitation
wavelengths, with numerical simulations of the time dependent Gross-Pitaevskii
equation. Our results show an anisotropy of the speed of soundComment: 3 figure
Solitons in a trapped spin-1 atomic condensate
We numerically investigate a particular type of spin solitons inside a
trapped atomic spin-1 Bose-Einstein condensate (BEC) with ferromagnetic
interactions. Within the mean field theory approximation, our study of the
solitonic dynamics shows that the solitonic wave function, its center of mass
motion, and the local spin evolutions are stable and are intimately related to
the domain structures studied recently in spin-1 Rb condensates. We
discuss a rotating reference frame wherein the dynamics of the solitonic local
spatial spin distribution become time independent.Comment: 8 pages, 8 color eps figure
Dynamical instability and domain formation in a spin-1 Bose condensate
We interpret the recently observed spatial domain formation in spin-1 atomic
condensates as a result of dynamical instability. Within the mean field theory,
a homogeneous condensate is dynamically unstable (stable) for ferromagnetic
(antiferromagnetic) atomic interactions. We find this dynamical instability
naturally leads to spontaneous domain formation as observed in several recent
experiments for condensates with rather small numbers of atoms. For trapped
condensates, our numerical simulations compare quantitatively to the
experimental results, thus largely confirming the physical insight from our
analysis of the homogeneous case.Comment: RevTex4, 4 pages with 3 color eps figure, to appear in Phys. Rev.
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