Equilibrium vortex formation in ultrarapidly rotating two-component Bose-Einstein condensates

Abstract

Equilibrium vortex formation in rotating binary Bose gases with a rotating frequency higher than the harmonic trapping frequency is investigated theoretically. We consider the system being evaporatively cooled to form condensates and a combined numerical scheme is applied to ensure the binary system being in an authentic equilibrium state. To keep the system stable against the large centrifugal force of ultrafast rotation, a quartic trapping potential is added to the existing harmonic part. Using the Thomas-Fermi approximation, a critical rotating frequency c is derived, which characterizes the structure with or without a central density hole. Vortex structures are studied in detail with rotation frequency both above and below c and with respect to the miscible, symmetrically separated, and asymmetrically separated phases in their nonrotating ground-state counterparts.

Ground-state and rotational properties of a two-component Bose–Einstein condensate in a harmonic plus quartic trap

“…We have found three different phases: (a) phase coexistence, (b) symmetric phase separation, (c) asymmetric phase separation. As seen in this figure, the phase boundary between phase coexistence and separation of the two components is, to a very good approximation, a straight line given by α 12 = α 2 , which agrees well with the results in [30]. Moreover, it is found that the quartic trap (with strength μ) has only a minimal effect on this boundary condition.…”

“…For the same reason which leads to a large self-interaction energy for the component 1, component 2 is always surrounded by component 1 in the region (b). However, the area of symmetric phase separation in the parameter space is much smaller than that in [30]. What might be the reason that caused this phenomenon?…”

“…One may gain some physical insight into this difference by considering the different types of quartic trap, which is isotropic in [30], while extreme anisotropic in our model. Thus, compared with the results reported in [30], although the boundary between (b) and (c) is more sensitive to μ, our numerical results are, to some extent, similar to the results of [30], that is, the area of phase (c) increases with the increasing of the strength of μ. Finally, it is noteworthy that in both regions (b) and (c), the density distributions are stretched along y-axis direction, and we attribute this to the special external potential considered here.…”

Stripes and honeycomb lattice of quantized vortices in rotating two-component Bose-Einstein condensates

“…It is noticeable that, when the all intercomponent and intracomponent couplings are equivalent, with the hamiltonian having an exact SU(2) symmetry, one peculiar structure of the vortex lattice appears, namely, honeycomb and double-core lattices. This has been observed in numerical simulations of the coupled Gross-Pitaevskii (GP) equations [7,10] and Monte-Carlo simulation of similar models [21]. Conversely, the theoretical analysis based on the lowest Landau level approximation has predicted that the vortex stripe, the alternating rows of vortices in each component, is the stable structure [6].…”

Pseudospin orders in the supersolid phases in binary Rydberg-dressed Bose-Einstein condensates

“…On the other hand, two-or multi-component system is of its own merit for fundamental interest especially in regards to the role of the inter-species interaction. For example, two-component BEC systems have been investigated on various properties by a number of groups [12][13][14][15][16][17][18]. Since the first experiment of two coexisting condensates of two different hyperfine states of 87 Rb was realized in 1997 [19] and as the Rydberg dressing technique is mature, it becomes possible to explore a SS state with internal degrees of freedom (SS with a basis or a SS superlattice).…”