We investigate the dynamics of turbulent flow in a two-dimensional trapped Bose-Einstein condensate by solving the Gross-Pitaevskii equation numerically. The development of the quantum turbulence is activated by the disruption of an initially embedded vortex quadrupole. By calculating the incompressible kinetic-energy spectrum of the superflow, we conclude that this quantum turbulent state is characterized by the Kolmogorov-Saffman scaling law in the wave-number space. Our study predicts the coexistence of two subinertial ranges responsible for the energy cascade and enstrophy cascade in this prototype of two-dimensional quantum turbulence.
We show that the five possible ordered states in a quantum spin-1/2 system with long-range exchange interactions: Néel, ladder, Peierls, coincidence, and domain states, can be realized in a binary Rydbergdressed BEC system in the supersolid phase. In such a system, blockade phenomenon is shown to also occur for pairs of different excited-state atoms, which results in similar intra-and inter-species long-range interactions between ground-state atoms. It suggests that a pseudo spin-1/2 system can be possibly formed in the ground state of ultracold rudibium.
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.
We investigate the dynamics of an unstable vortex ring in a pancake-shaped Bose-Einsten condensate by solving the Gross-Pitaevskii equation numerically. It is found that a quasisteady turbulent state with long relaxation time can be achieved through the disruption of a perturbed vortex ring in the condensate owing to the bending-wave instability. We verify that this quantum turbulent state is characterized by Kolmogorov energy spcetrum.
We investigate the spontaneous generation of crystallized topological defects via the combining effects of fast rotation and rapid thermal quench on the spin-1 Bose-Einstein condensates. By solving the stochastic projected Gross-Pitaevskii equation, we show that, when the system reaches equilibrium, a hexagonal lattice of skyrmions, and a square lattice of half-quantized vortices can be formed in a ferromagnetic and antiferromagnetic spinor BEC, respetively, which can be imaged by using the polarization-dependent phase-contrast method.PACS numbers: 03.75. Lm, 03.75.Mn, 03.75.Kk, 05.10.Gg Topological defects are a manifestation of spontaneously broken symmetries [1]. Formation and observation of topological defects are one of the most fundamental and fascinating topics in various aspects of physics, ranging from condensed matter physics to cosmology. However, owing to the limitation of energy scales in the earth-bound physics experiments, topological defects are mostly created and observed in the condensed matter systems. For example, magnetic domains walls of magnetized material and string defects in 3 He superfluid phase transitions have been extensively studied [2].Recently, owing to the realization of spinor BoseEinstein condensate (BEC) of alkali atoms in optical trap [3,4], the creation of topological defects in ultracold atomic systems has become possible. A spinor BEC is fully characterized by the spin degrees of freedom and behaves as a vector in the spin space. Theoretical studies for the spinor BEC were pioneered by Ho [5], and independently by Ohmi and Machida [6]. More recently, spinor BECs with F > 1 [7][8][9] or with long range dipolar interaction [10,11] have also been theoretically investigated. In general, the physical behavior of the spinor BEC depends crucially on its magnetic properties, such that the interplay between the superfluidity and magnetism of the condensate makes the spinor BEC a candidate to exhibit a variety of nontrivial ordered states, such as the skyrmions So far, all theoretical studies regarding the formation of topological defects in spinor BEC appeal to manipulate the external and internal degrees of freedom of the condensed atoms at zero temperature. On the other hand, according to the Kibble-Zurek scenario, topological defects can also be created through phase transitions at finite temperatures, which are fundamentally caused by spontaneous symmetry breaking and thermal fluctuations near the critical point. In this paper, we show that it is possible to create crystalline orders of skyrmions and fractional vortices simply by thermally quenching a rotating spin-1 BEC. This enables us to probe into the very fundamental aspects of topological defects without any engineering of dynamical processes, since evaporative cooling is prerequisite in creating BECs and the methods of rotating condensates have been well developed in a variety of ultracold atoms experiments. In the framework of mean field theory, the dynamics of a BEC at nonzero temperatures can be described by the s...
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