Simulations of Quantized Vortices andQuantum Turbulence using theGross-Pitaevskii equation

Ionut Danaila

Michikazu Kobayashi, Ionut Danaila, Corentin Lothodé +3 more

A. Bershadskii

Transition to condensate state in the degenerate gas of bosons is studied using the Gross-Pitaevskii equation. It is shown that adiabatic invariance of an enstrophy (mean squared vorticity) based on a generalized vorticity $curl (|ψ|^2 {\bf v})/|ψ|^2$, controls dynamics of the transitional turbulence just before formation of the condensate with its tangles of quantized vortices ($|ψ|^2 {\bf v}$ is the weighted velocity field defined on the macroscopic wave function $ψ$). Scaling of the angle-averaged occupation number spectrum, $N_k \sim k^{-1}$, has been obtained for the free developing transitional turbulence for the weak nonlinear (and completely disordered) initial conditions. Results of the three-dimensional numerical simulations have been used to support the theoretical consideration.

Makoto Tsubota, Kenichi Kasamatsu

Takuya Kusumura, Hiromitsu Takeuchi, Makoto Tsubota

We discuss the configurations of vortices in two-dimensional quantum turbulence, studying energy spectrum of superfluid velocity and correlation functions with the distance between two vortices. We apply the above method to quantum turbulence described by Gross-Pitaevskii equation in Bose-Einstein condensates. We make two-dimensional quantum turbulence from many dark solitons through the dynamical instability. A dark soliton is unstable and decays into vortices in two- and three-dimensional systems. In our work, we propose a method of discriminating between the uncorrelated turbulence and the correlated turbulence. We decompose the energy spectrum into two terms, namely the self-energy spectrum E self (k) made by individual vortices and the interactive energy spectrum E int (k) made by interference of two vortices. The uncorrelated turbulence is defined as turbulence with E int (k)≪E self (k), while the correlated turbulence is turbulence where E int (k) is not much smaller than E self (k). Our simulations show that in the decay of dark solitons, the vortices created consist of correlated pairs of opposite circulation vortices, leading to the correlated turbulence.

Michikazu Kobayashi, Makoto Tsubota

We investigated dynamics of superfluid turbulence by the Gross-Pitaevskii equation and its relation to conventional classical turbulence. We introduced the dissipation term which is effective only in the scale smaller than the core size of quantized vortices, and found that the energy spectrum of superfluid turbulence was consistent with the Kolmogorov law which is one of the most important statistical laws of classical turbulence.