Transition to quantum turbulence in finite-size superfluids

Abstract

A novel concept of quantum turbulence in finite size superfluids, such as trapped bosonic atoms, is discussed. We have used an atomic 87 Rb Bose-Einstein condensate (BEC) to study the emergence of this phenomenon. In our experiment, the transition to the quantum turbulent regime is characterized by a tangled vortex lines formation, controlled by the amplitude and time duration of the excitation produced by an external oscillating field. A simple model is suggested to account for the experimental observations. The transition from the nonturbulent to the turbulent regime is a rather gradual crossover. But it takes place in a sharp enough way, allowing for the definition of an effective critical line separating the regimes. Quantum turbulence emerging in a finite-size superfluid may be a new idea helpful for revealing important features associated to turbulence, a more general and broad phenomenon. Amplitude versus elapsed time diagram of magnetically excited BEC superfluid, presenting the evolution from the nonturbulent regime, with well separated vortices, to the turbulent regimes, with tangled vortices

Realization of inverse Kibble–Zurek scenario with trapped Bose gases

“…We employ the same experimental setup as in the experiments studying quantum turbulence of trapped 87 Rb atoms [27][28][29]. The gas of 87 Rb atoms is cooled down to the state where almost all atoms, up to 70% are condensed, with the number of atoms in Bose-Einstein condensate being N ≈ 2 × 10 5 .…”

“…After forming equilibrium Bose-Einstein condensate, the atomic cloud is subject to an oscillatory trap modulation that shakes the condensate without imposing a rotation axis, but preserving the cloud isotropy [30]. As in our previous papers [27][28][29], we use the perturbing potential…”

“…This perturbing potential distorts the atomic cloud with a combination of deformations, rotations, and displacements [27][28][29]. The modulation amplitude and time can be varied in a wide range, thus, varying the energy injected into the system.…”

“…In the typical time-of-flight procedure, the chaotization [34] and nonadiabatic [35] effects do not occur and the expanding atomic cloud preserves the features of the state inside the trap [27][28][29].…”

“…Since no single rotation axis is imposed onto the system, the creation of vortices and anti-vortices is equally likely. The typical situation is that vortices and anti-vortices appear together in groups [27][28][29]. The vortex-antivortex pairs do not form bound dipoles, being not correlated with each other, except having opposite vorticities.…”