Kyoto, Japan -- Lord Kelvin theorized in 1880 that stimulating a thin vortex line would produce a helical deformation, later known as a Kelvin wave. While these waves have been observed in classical fluids like water and air, their existence in quantum fluids has remained largely theoretical due to the extreme difficulty of observing them in a lab experiment.
Now a team of scientists from Japan has demonstrated controlled mechanical oscillations of quantum vortex core lines in superfluid helium. Publishing their results in Nature Physics, the group's finding showcases the excitation and visualization of these helical waves on quantum vortices.
"Quantum fluids are ideal systems that closely resemble the fluids Lord Kelvin had in mind," explains team leader Yosuke Minowa of Kyoto University. "However, the inability to both excite and observe Kelvin waves in these fluids has limited our understanding of them."
The research team, also including Osaka University and Osaka Metropolitan University, employed nanoparticles produced via laser ablation, where a strong laser pulse causes intense melting and vaporization of a material. The nanoparticles, some of which become electrically charged, naturally attach to each other along the vortex lines in superfluid helium.
By applying an alternating current field to the vortex decorated with these nanoparticles, the team successfully stimulated oscillations in the quantum vortex, leading to the excitation of Kelvin waves. A dual-camera system was then used to reconstruct the three-dimensional dynamics of these waves, revealing their intricate helical structures.
"Our ability to control and manipulate these vortices marks a significant shift. We can now not only observe but actively engage with the dynamics of quantum vortices," says Minowa.
This result holds promise for deeper exploration into quantum fluid dynamics, including the energy dissipation processes and interactions among multiple vortices. The team's unique integration of photonic techniques with superfluid helium was a key factor in their success.
