Vorticity and quantum turbulence in the merging of superfluid Helium nanodroplets

Abstract

We have studied the merging of two ${}^4$He droplets at zero temperature, caused by their Van der Waals mutual attraction. During the early stages of the merging, density structures appear which closely match the experimental observations by Vicente et al. [J. Low Temp. Phys. 121, 627 (2000)]. When the droplets are merging, quantized vortex-antivortex ring pairs nucleate at the surface and annihilate inside the merged droplet producing a roton burst. We also observe the nucleation of quantized vortex-antivortex rings that wrap the droplet surface and remain localized on the surface until they eventually decay into short-wavelength surface waves. Analysis of the kinetic energy spectrum discloses the existence of a regime where turbulence caused by vortex interaction and annihilation is characterized by a Kolmogorov power law. This is followed by another regime where roton radiation (produced by vortex-antivortex annihilation) dominates, whose hallmark is a weak, turbulent surface dynamics. We suggest that similar processes might appear in superfluid helium droplets after they capture impurities or if they are produced by hydrodynamic instability of a liquid jet. Experiments on collisions between recently-discovered self-bound Bose-Einstein condensates should display a similar phenomenology.

6 pages, 5 figures; revised version

References in corpus (9)

• Quantum liquid droplets in a mixture of Bose-Einstein condensates
• Introduction to quantum turbulence
• Emergence of a Turbulent Cascade in a Quantum Gas
• Collisions of self-bound quantum droplets
• Energy spectra of vortex distributions in two-dimensional quantum turbulence
• Density Functional Theory of doped superfluid liquid helium and nanodroplets
• Turbulent velocity spectra in superfluid flows
• Classical and quantum regimes of two-dimensional turbulence in trapped Bose-Einstein condensates
• Quantum Monte Carlo study of a vortex in superfluid ${}^4$He and search for a vortex state in the solid

Cited by in corpus (10)

• The dispersion relation of Landau elementary excitations and the thermodynamic properties of superfluid ${}^4$He
• Vortex properties in the extended supersolid phase of dipolar Bose-Einstein condensates
• Towards a QMC-based density functional including finite-range effects: excitation modes of a ${}^{39}$K quantum droplet
• Coexistence of vortex arrays and surface capillary waves in spinning prolate superfluid He-4 nanodroplets
• Bound-state spectrum of an impurity in a quantum vortex
• Nanoscopic jets and filaments of superfluid He-4 at zero temperature: a DFT study
• Dynamic instabilities and turbulence of merged rotating Bose-Einstein condensates
• Merging of superfluid Helium nanodroplets with vortices
• Ab-initio Quantum Monte Carlo study of ultracold atomic mixtures
• Dilute quantum liquid in a K-Rb Bose mixture