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Register a new userVinen turbulence via the decay of multicharged vortices in trapped atomic Bose-Einstein condensates
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We investigate a procedure to generate turbulence in a trapped Bose-Einstein condensate which takes advantage of the decay of multicharged vortices. We show that the resulting singly-charged vortices twist around each other, intertwined in the shape of helical Kelvin waves, which collide and undergo vortex reconnections, creating a disordered vortex state. By examining the velocity statistics, the energy spectrum, the correlation functions and the temporal decay, and comparing these properties with the properties of ordinary turbulence and observations in superfluid helium, we conclude that this disordered vortex state can be identified with the `Vinen regime of turbulence which has been discovered in the context of superfluid helium.
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The decay of multicharged vortices in trapped Bose-Einstein condensates may lead to a disordered vortex state consistent with the Vinen regime of turbulence, characterized by an absence of large-scale flow and an incompressible kinetic energy spectrum $Epropto k^{-1}$. In this work, we study numerically the dynamics of a three-dimensional harmonically trapped Bose-Einstein condensate excited to a Vinen regime of turbulence through the decay of two doubly-charged vortices. First, we study the momentum distribution and observe the emergence of a power-law behavior $n(k)propto k^{-3}$ consistent with the coexistence of wave turbulence. We also study the kinetic energy and particle fluxes, which allows us to identify a direct particle cascade associated with the turbulent stage.
Reconnections and interactions of filamentary coherent structures play a fundamental role in the dynamics of fluids, plasmas and nematic liquid crystals. In fluids, vortex reconnections redistribute energy and helicity among the length scales and induce fine-scale turbulent mixing. Unlike ordinary fluids where vorticity is a continuous field, in quantum fluids vorticity is concentrated into discrete (quantized) vortex lines turning vortex reconnections into isolated events, making it conceptually easier to study. Here we report experimental and numerical observations of three-dimensional quantum vortex interactions in a cigar-shaped atomic Bose-Einstein Condensate (BEC). In addition to standard reconnections, already numerically and experimentally observed in homogeneous systems away from boundaries, we show that double reconnections, rebounds and ejections can also occur as a consequence of the non-homogeneous, confined nature of the system.
We analyse, theoretically and experimentally, the nature of solitonic vortices (SV) in an elongated Bose-Einstein condensate. In the experiment, such defects are created via the Kibble-Zurek mechanism, when the temperature of a gas of sodium atoms is quenched across the BEC transition, and are imaged after a free expansion of the condensate. By using the Gross-Pitaevskii equation, we calculate the in-trap density and phase distributions characterizing a SV in the crossover from an elongate quasi-1D to a bulk 3D regime. The simulations show that the free expansion strongly amplifies the key features of a SV and produces a remarkable twist of the solitonic plane due to the quantized vorticity associated with the defect. Good agreement is found between simulations and experiments.
Vortex is a topological defect with a quantized winding number of the phase in superfluids and superconductors. Here, we investigate the crystallized (triangular, square, honeycomb) and amorphous vortices in rotating atomic-molecular Bose-Einstein condensates (BECs) by using the damped projected Gross-Pitaevskii equation. The amorphous vortices are the result of the considerable deviation induced by the interaction of atomic-molecular vortices. By changing the atom-molecule interaction from attractive to repulsive, the configuration of vortices can change from an overlapped atomic-molecular vortices to carbon-dioxide-type ones, then to atomic vortices with interstitial molecular vortices, and finally into independent separated ones. The Raman detuning can tune the ratio of the atomic vortex to the molecular vortex. We provide a phase diagram of vortices in rotating atomic-molecular BECs as a function of Raman detuning and the strength of atom-molecule interaction.
We study two-dimensional quantum turbulence in miscible binary Bose-Einstein condensates in either a harmonic trap or a steep-wall trap through the numerical simulations of the Gross-Pitaevskii equations. The turbulence is generated through a Gaussian stirring potential. When the condensates have unequal intra-component coupling strengths or asymmetric trap frequencies, the turbulent condensates undergo a dramatic decay dynamics to an interlaced array of vortex-antidark structures, a quasi-equilibrium state, of like-signed vortices with an extended size of the vortex core. The time of formation of this state is shortened when the parameter asymmetry of the intra-component couplings or the trap frequencies are enhanced. The corresponding spectrum of the incompressible kinetic energy exhibits two noteworthy features: (i) a $k^{-3}$ power-law around the range of the wave number determined by the spin healing length (the size of the extended vortex-core) and (ii) a flat region around the range of the wave number determined by the density healing length. The latter is associated with the small scale phase fluctuation relegated outside the Thomas-Fermi radius and is more prominent as the strength of intercomponent interaction approaches the strength of intra-component interaction. We also study the impact of the inter-component interaction to the cluster formation of like-signed vortices in an elliptical steep-wall trap, finding that the inter-component coupling gives rise to the decay of the clustered configuration.
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