  In superfluid helium, vorticity is quantized and constrained on line-like
phase singularities, called quantum or quantized vortices. By visualizing the
motion of sub-micron frozen particles in superfluid $^{4}$He, we directly
observe for the first time the helical Kelvin waves excited after quantized
vortex reconnections. We compare the data with self-similar solutions of vortex
filament models. We report the results in a fluid dynamic video.
