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Ferromagnetic Resonance in Spinor Dipolar Bose--Einstein Condensates  [PDF]
Masashi Yasunaga,Makoto Tsubota
Physics , 2010, DOI: 10.1103/PhysRevA.83.013618
Abstract: We used the Gross--Pitaevskii equations to investigate ferromagnetic resonance in spin-1 Bose--Einstein condensates with a magnetic dipole-dipole interaction. By introducing the dipole interaction, we obtained equations similar to the Kittel equations used to represent ferromagnetic resonance in condensed matter physics. These equations indicated that the ferromagnetic resonance originated from dipolar interaction, and that the resonance frequency depended upon the shape of the condensate. Furthermore, spin currents driven by spin diffusions are characteristic of this system.
Can Spinor Dipolar Effects be Observed in Bose-Einstein Condensates?  [PDF]
Yuki Kawaguchi,Hiroki Saito,Masahito Ueda
Physics , 2006, DOI: 10.1103/PhysRevLett.98.110406
Abstract: Weak dipolar effects in atomic Bose-Einstein condensates (BECs) have recently been predicted to develop spin textures. However, observation of these effects requires magnetic field as low as $\sim 10 \mu$G for spin-1 alkali BECs, so that they are not washed out by the Zeeman effect. We present a scheme to observe the magnetic dipole-dipole interaction in alkali BECs under a realistic magnetic field of $\sim 100$ mG. Our scheme enables us to extract genuine dipolar effects and should apply also to $^{52}$Cr BECs.
How to observe dipolar effects in spinor Bose-Einstein condensates  [PDF]
Krzysztof Gawryluk,Kai Bongs,Miroslaw Brewczyk
Physics , 2010, DOI: 10.1103/PhysRevLett.106.140403
Abstract: We study a spinor condensate of alkali atoms in F = 1 hyperfine state under the presence of an oscillating magnetic field. We find resonances which, due to the dipolar interactions, magnify the transfer of atoms from mF = 1 to mF = 0 Zeeman sublevel. These resonances occur at magnetic fields of the order of milligaus and are broad enough to enable observation of the famous Einstein-de Haas effect, which is solely a dipolar effect, in systems of cold alkali gases.
Spin echo in spinor dipolar Bose-Einstein condensates  [PDF]
Masashi Yasunaga,Makoto Tsubota
Physics , 2008, DOI: 10.1103/PhysRevLett.101.220401
Abstract: We theoretically propose and numerically realize spin echo in a spinor Bose--Einstein condensate (BEC). We investigate the influence on the spin echo of phase separation of the condensate. The equation of motion of the spin density exhibits two relaxation times. We use two methods to separate the relaxation times and hence demonstrate a technique to reveal magnetic dipole--dipole interactions in spinor BECs.
Effective field theory for spinor dipolar Bose Einstein condensates  [PDF]
M. Takahashi,Sankalpa Ghosh,T. Mizushima,K. Machida
Physics , 2008, DOI: 10.1140/epjb/e2009-00016-8
Abstract: We show that the effective theory of long wavelength low energy behavior of a dipolar Bose-Einstein condensate(BEC) with large dipole moments (treated as a classical spin) can be modeled using an extended Non-linear sigma model (NLSM) like energy functional with an additional non-local term that represents long ranged anisotropic dipole-dipole interaction. Minimizing this effective energy functional we calculate the density and spin-profile of the dipolar Bose-Einstein condensate in the mean-field regime for various trapping geometries. The resulting configurations show strong intertwining between the spin and mass density of the condensate, transfer between spin and orbital angular momentum in the form of Einstein-de Hass effect, and novel topological properties. We have also described the theoretical framework in which the collective excitations around these mean field solutions can be studied and discuss some examples qualitatively.
Spinor dipolar Bose-Einstein condensates; Classical spin approach  [PDF]
M. Takahashi,Sankalpa Ghosh,T. Mizushima,K. Machida
Physics , 2007, DOI: 10.1103/PhysRevLett.98.260403
Abstract: 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.
Internal Josephson Effects in Spinor Dipolar Bose--Einstein Condensates  [PDF]
Masashi Yasunaga,Makoto Tsubota
Physics , 2009, DOI: 10.1103/PhysRevA.81.023624
Abstract: We theoretically study the internal Josephson effect, which is driven by spin exchange interactions and magnetic dipole-dipole interactions, in a three-level system for spin-1 Bose--Einstein condensates, obtaining novel spin dynamics. We introduce single spatial mode approximations into the Gross--Pitaevskii equations and derive the Josephson type equations, which are analogous to tunneling currents through three junctions between three superconductors. From an analogy with two interacting nonrigid pendulums, we identify unique varied oscillational modes, called the 0--$\pi$, 0--$running$, $running$--$running$, $2n\pi & running$--$2\pi$, $single nonrigid pendulum$, and $two rigid pendulums$ phase modes. These Josephson modes in the three states are expected to be found in real atomic Bose gas systems.
Spinor Bose-Einstein condensates  [PDF]
Yuki Kawaguchi,Masahito Ueda
Physics , 2010, DOI: 10.1016/j.physrep.2012.07.005
Abstract: An overview on the physics of spinor and dipolar Bose-Einstein condensates (BECs) is given. Mean-field ground states, Bogoliubov spectra, and many-body ground and excited states of spinor BECs are discussed. Properties of spin-polarized dipolar BECs and those of spinor-dipolar BECs are reviewed. Some of the unique features of the vortices in spinor BECs such as fractional vortices and non-Abelian vortices are delineated. The symmetry of the order parameter is classified using group theory, and various topological excitations are investigated based on homotopy theory. Some of the more recent developments in a spinor BEC are discussed.
Symmetry-breaking magnetization dynamics of spinor dipolar Bose-Einstein condensates  [PDF]
Shoichi Hoshi,Hiroki Saito
Physics , 2009, DOI: 10.1103/PhysRevA.81.013627
Abstract: Symmetry-breaking magnetization dynamics of a spin-1 Bose-Einstein condensate (BEC) due to the dipole-dipole interaction are investigated using the mean-field and Bogoliubov theories. When a magnetic field is applied along the symmetry axis of a pancake-shaped BEC in the m = 0 hyperfine sublevel, transverse magnetization develops breaking the chiral or axial symmetry. A variety of magnetization patterns are formed depending on the strength of the applied magnetic field. The proposed phenomena can be observed in 87Rb and 23Na condensates.
Spontaneous Circulation in Ground-State Spinor Dipolar Bose-Einstein Condensates  [PDF]
Yuki Kawaguchi,Hiroki Saito,Masahito Ueda
Physics , 2006, DOI: 10.1103/PhysRevLett.97.130404
Abstract: We report on a study of the spin-1 ferromagnetic Bose-Einstein condensate with magnetic dipole-dipole interactions. By solving the non-local Gross-Pitaevskii equations for this system, we find three ground-state phases. Moreover, we show that a substantial orbital angular momentum accompanied by chiral symmetry breaking emerges spontaneously in a certain parameter regime. We predict that all these phases can be observed in the spin-1 $^{87}$Rb condensate by changing the number of atoms or the trap frequency.
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