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Register a new userVortex splitting and phase separating instabilities of coreless vortices in F=1 spinor Bose-Einstein condensates
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The low lying excitations of coreless vortex states in F = 1 spinor Bose-Einstein condensates (BECs) are theoretically investigated using the Gross-Pitaevskii and Bogoliubov-de Gennes equations. The spectra of the elementary excitations are calculated for different spin-spin interaction parameters and ratios of the number of particles in each sublevel. There exist dynamical instabilities of the vortex state which are suppressed by ferromagnetic interactions, and conversely, enhanced by antiferromagnetic interactions. In both of the spin-spin interaction regimes, we find vortex splitting instabilities in analogy with scalar BECs. In addition, a phase separating instability is found in the antiferromagnetic regime.
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We study the energetic and dynamic stability of coreless vortices in nonrotated spin-1 Bose-Einstein condensates, trapped with a three-dimensional optical potential and a Ioffe-Pritchard field. The stability of stationary vortex states is investigated by solving the corresponding Bogoliubov equations. We show that the quasiparticle excitations corresponding to axisymmetric stationary states can be taken to be eigenstates of angular momentum in the axial direction. Our results show that coreless vortex states can occur as local or global minima of the condensate energy or become energetically or dynamically unstable depending on the parameters of the Ioffe-Pritchard field. The experimentally most relevant coreless vortex state containing a doubly quantized vortex in one of the hyperfine spin components turned out to have very non-trivial stability regions, and especially a quasiperiodic dynamic instability region which corresponds to splitting of the doubly quantized vortex.
Extended Gross-Pitaevskii equations for the rotating F=2 condensate in a harmonic trap are solved both numerically and variationally using trial functions for each component of the wave function. Axially-symmetric vortex solutions are analyzed and energies of polar and cyclic states are calculated. The equilibrium transitions between different phases with changing of the magnetization are studied. We show that at high magnetization the ground state of the system is determined by interaction in density channel, and at low magnetization spin interactions play a dominant role. Although there are five hyperfine states, all the particles are always condensed in one, two or three states. Two novel types of vortex structures are also discussed.
We observe interlaced square vortex lattices in rotating two-component dilute-gas Bose-Einstein condensates (BEC). After preparing a hexagonal vortex lattice in a single-component BEC in an internal state $|1>$ of $^{87}$Rb atoms, we coherently transfer a fraction of the superfluid to a different internal state $|2>$. The subsequent evolution of this pseudo-spin-1/2 superfluid towards a state of offset square lattices involves an intriguing interplay of phase-separation and -mixing dynamics, both macroscopically and on the length scale of the vortex cores, and a stage of vortex turbulence. Stability of the square lattice structure is confirmed via the application of shear perturbations, after which the structure relaxes back to the square configuration. We use an interference technique to show the spatial offset between the two vortex lattices. Vortex cores in either component are filled by fluid of the other component, such that the spin-1/2 order parameter forms a Skyrmion lattice.
We experimentally investigate and analyze the rich dynamics in F=2 spinor Bose-Einstein condensates of Rb87. An interplay between mean-field driven spin dynamics and hyperfine-changing losses in addition to interactions with the thermal component is observed. In particular we measure conversion rates in the range of 10^-12 cm^3/s for spin changing collisions within the F=2 manifold and spin-dependent loss rates in the range of 10^-13 cm^3/s for hyperfine-changing collisions. From our data we observe a polar behavior in the F=2 ground state of Rb87, while we measure the F=1 ground state to be ferromagnetic. Furthermore we see a magnetization for condensates prepared with non-zero total spin.
Topological phase imprinting is a well-established technique for deterministic vortex creation in spinor Bose-Einstein condensates of alkali metal atoms. It was recently shown that counter-diabatic quantum control may accelerate vortex creation in comparison to the standard adiabatic protocol and suppress the atom loss due to nonadiabatic transitions. Here we apply this technique, assisted by an optical plug, for vortex pumping to theoretically show that sequential phase imprinting up to 20 cycles generates a vortex with a very large winding number. Our method significantly increases the fidelity of the pump for rapid pumping compared to the case without the counter-diabatic control, leading to the highest angular momentum per particle reported to date for the vortex pump. Our studies are based on numerical integration of the three-dimensional multi-component Gross-Pitaevskii equation which conveniently yields the density profiles, phase profiles, angular momentum, and other physically important quantities of the spin-1 system. Our results motivate the experimental realization of the vortex pump and studies of the rich physics it involves.
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