Chaotic few-body vortex dynamics in rotating Bose-Einstein condensates

Abstract

We investigate a small vortex-lattice system of four co-rotating vortices in an atomic Bose-Einstein condensate and find that the vortex dynamics display chaotic behaviour after a system quench introduced by reversing the direction of circulation of a single vortex through a phase-imprinting process. By tracking the vortex trajectories and Lyapunov exponent, we show the onset of chaotic dynamics is not immediate, but occurs at later times and is accelerated by the close-approach and separation of all vortices in a scattering event. The techniques we develop could potentially be applied to create locally induced chaotic dynamics in larger lattice systems as a stepping stone to study the role of chaotic events in turbulent vortex dynamics. arXiv:1812.04759v1 [cond-mat.quant-gas]

Deep learning based quantum vortex detection in atomic Bose-Einstein condensates

“…The machine learning model can also be straightforwardly integrated with a GPU solver of the Gross-Pitaevskii equation which would eliminate the need to transfer data between CPU and GPU [65]. As a possible next step the vortex detector could be combined with a tracking algorithm enabling the study of real-time dynamics of vortices in BECs such as in references [14,50,54].…”

“…have a winding number with the same sign, which is determined by the rotation frequency Ω. Situations where vortices of different rotation directions co-exist can be created for instance by forcing the superfluid to flow around an obstacle potential [47,48] or through the process of phase imprinting [49,50,51,52,53]. In the latter case, a single vortex centered at (x 0 , y 0 ) is generated by applying a phase mask φ IMP (r) = arctan (y − y 0 , x − x 0 ) with a 2π phase winding in the desired direction.…”

“…The timeevolution of configurations with multiple vortices of unequal rotation direction features interesting out-of-equilibrium processes such as vortex -antivortex annihilation and the emergence of other low energy excitations. Furthermore, it has been shown that a three and four vortex-system with one counter-rotating vortex can already lead to chaotic dynamics [14,50,54] and that large vortex systems can give rise to quantum turbulence [5,19,55,56]. Figure 1(c)-(d) displays a density and phase profile snapshot during a representative time evolution after phase imprinting additional anti-vortices.…”

“…The latter are obtained by a brute-force detection method described in detail in Appendix A. Our training and test data is comprised of both ground state and out-of-equilibrium configurations which are obtained through numerical simulations of the GPE (see equation ( 1)) with parameter values sampled uniformly from the range g ∈ [50,600] for the interaction strength and Ω ∈ [0.65, 0.95] for the rotation frequency. The obtained density and phase profiles are normalized such that their pixels lie between [0, 1] before being input to the convolutional neural network (CNN).…”

Vortex patterns of atomic Bose-Einstein condensates in a density-dependent gauge potential

“…Vortices central role in superfluidity continues to attract theoretical and experimental interest in the macroscopic dynamics of these excitations. Early work focussed on studying the fundamental properties of the rotating system [13][14][15], while more recent work has focussed on understanding the effect of anisotropic trapping [16], vortex lattice [17,18], and chaotic [19] dynamics. Focus has also been on the structure and dynamics of vortices in condensates at finite temperature including non-equilibrium effects [20,21], multi-component systems which have been shown to possess a rich vortex physics [23][24][25][26][27][28] and the on-going quest to understand quantum turbulence [29,30].…”