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Quantum turbulence by vortex stirring in a spinor Bose-Einstein condensate (1309.6218v1)

Published 24 Sep 2013 in cond-mat.quant-gas

Abstract: We introduce a novel mechanism to develop a turbulent flow in a spinor Bose-Einstein condensate, consisting in the stirring of a single line vortex by means of an external magnetic field. We find that density and velocity fluctuations have white-noise power spectra at large frequencies and that Kolmogorov 5/3 law is obeyed in the turbulent region. As the stirring is turned off, the flow decays to an agitated non-equilibrium state that shows an energy bottleneck crossover at small length scales. We demonstrate our findings by numerically solving two-state spinor coupled 3D Gross-Pitaevskii equations. We suggest that this mechanism may be experimentally implemented in spinor ultracold gases confined by optical traps.

Summary

  • The paper introduces a vortex stirring method using modulated magnetic fields to induce quantum turbulence in spinor Bose-Einstein condensates, enabling controlled exploration of complex superfluid flows.
  • It employs GPU-accelerated Gross-Pitaevskii simulations to reveal turbulence features including a white-noise power spectrum at high frequencies and adherence to Kolmogorov’s 5/3 law.
  • The study uncovers a non-equilibrium stationary state post stirring whose energy decay and vortex dynamics provide insightful implications for future quantum turbulence experiments.

Quantum Turbulence in Spinor Bose-Einstein Condensates via Vortex Stirring

The paper titled "Quantum turbulence by vortex stirring in a spinor Bose-Einstein condensate" explores the dynamics of quantum turbulence (QT) in spinor Bose-Einstein condensates (BECs) induced by stirring a single line vortex using an external magnetic field. This paper contributes to the ongoing research in quantum fluids by extending our understanding of turbulence generation, statistical steady states, and decay in quantum systems.

Key Findings and Methodology

The authors propose a novel approach to induce turbulence within a spinor BEC by stirring a single quantum vortex with a modulated magnetic field. This mechanism introduces turbulence characterized by density and velocity fluctuations that exhibit a white-noise power spectrum at high frequencies and comply with Kolmogorov's 5/3 law in turbulent regions. The paper utilizes numerical solutions of the three-dimensional Gross-Pitaevskii equations for two-state spinor coupled systems to substantiate their findings.

  • Generation of Turbulence: The turbulence is initiated through vortex stirring facilitated by a dynamic external magnetic field. The magnetic field modulation creates complex superfluid flow patterns in both spin components of the spinor BEC, producing vortex line and ring formations that do not dissipate readily due to the absence of viscosity in GP systems.
  • Statistical Characteristics: The induced turbulence is analyzed by monitoring the power spectra of density and velocity field fluctuations. While the turbulent flow decays post-excitation, it stabilizes into a non-equilibrium stationary state characterized by an energy bottleneck on smaller scales. The statistical state of the spinor BEC reflects properties akin to those observed in classical turbulence but differentiated by the unique quantum susceptibilities of the system.
  • Energy Decay and Nucleation: Upon cessation of the stirring action, the system transitions into a long-lasting agitated state. This decay presents important insights into the energy dissipation processes within quasi-stable turbulent structures in superfluid substances.

Numerical and Experimental Considerations

The paper employs a robust computational model to track the dynamics of vortices under the influence of the magnetic fields, adopting a numerical scheme that proceeds via the GPU-accelerated solution of the GP equations. By setting initial conditions that include a line vortex of topological charge, the authors ensure a starting point for meaningful vortex interactions, paving the way toward understanding vortex dynamics in an inviscid and low-temperature environment.

The authors suggest that the experimental realization of this mechanism is feasible with current cold atom technology using optical traps. The parameters utilized in the simulations reflect experimental conditions accessible with ultracold gases confined by such traps, making the findings relevant and impactful for the design of future quantum turbulence experiments.

Implications and Future Directions

The insights derived from this research carry substantial implications for the field of quantum hydrodynamics. The ability to induce and paper turbulence in spinor BECs fosters advancements in understanding macroscopic quantum phenomena and facilitates the exploration of universal behaviors observed in classical and quantum fluids.

Future work could delve into the quantitative characterization of turbulence decay mechanisms within interacting quantum systems and the role of thermal fluctuations in the nonlinear dynamics of vortices. This research direction might benefit from incorporating dissipation models into the superfluid description to simulate more realistic quantum turbulence scenarios aligned with experimental observations. Additionally, extending the models to include interactions with thermal clouds could provide a comprehensive picture of energy transfer and dissipation in cold atom systems.

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