Direct excitation of Kelvin waves on quantized vortices

Helices and spirals, prevalent across various physical systems, play a crucial role in characterizing symmetry, describing dynamics and enabling unique functionalities, all stemming from their inherent simplicity and chiral nature. Helical excitations on quantized vortices, referred to as Kelvin waves, are one example of such a physical system. Kelvin waves play a vital role in energy dissipation within inviscid quantum fluids. However, deliberately exciting Kelvin waves has proven to be challenging. Here we introduce a controlled method for exciting Kelvin waves on a quantized vortex in superfluid helium-4. We used a charged nanoparticle that oscillates when driven by a time-varying electric field to stimulate Kelvin waves on the vortex. Confirmation of the helical nature of Kelvin waves was achieved through three-dimensional image reconstruction, which provided visual evidence of their complex dynamics. Additionally, we determined the dispersion relation and the phase velocity of the Kelvin wave and identified the vorticity direction, thus enhancing our understanding of quantum fluid behaviour. This work elucidates the dynamics of Kelvin waves and initiates an approach for manipulating and observing quantized vortices in three dimensions, thereby opening avenues for exploring quantum fluidic systems.