Friction Found in Superfluid Helium near Absolute Zero

Friction shouldn’t appear in superfluid helium at temperatures near absolute zero, but that’s just what researchers at Aalto University in Finland report observing in a new experiment. Understanding the causes and effects of the friction could pave the way for explorations into the composition of neutron stars and our universe, according to the research team, and could also be invaluable for curtailing the production of heat and unwanted glitches in quantum computer components.

“For now, we have to study the phenomenon itself more in-depth before we can have insight exhaustive enough to be applied to experimental research and developing technologies,” says Jere Makinen, a doctoral researcher at the university.

The researchers rotated a container filled with superfluid helium-3 isotopes at temperatures near absolute zero temperature. The rotating fluid mimics the motion of solid bodies, creating tiny, identical hurricanes called vortices. When the vortices are in stable and ordered laminar motion at extremely low temperature—as opposed in endlessly chaotic turbulence—there should be no friction nor means for a vortex to transfer any kinetic energy to its surroundings. Yet that is exactly what Makinen and his supervisor Dr. Vladimir Eltsov observed.

The two suspect that the source of the friction is quasi-particles trapped in the cores of the vortices. When the vortices accelerate, the particles gain kinetic energy which dissipates to surrounding particles and creates friction. “In turbulent systems, kinetic energy always dissipates from the motion of vortices, but up to now everyone had thought that when vortices are in laminar motion the dissipation of energy is zero at zero temperature. But it turns out, it’s not,” says Eltsov.

Makinen compares the dissipation of heat to shaking a box full of table tennis balls that gain kinetic energy from the moving box and the other balls bouncing around. Preventing the vortices from dissipating heat and therefore friction, could, for example, enhance the performance of and the ability to retain data in superconducting components used to construct quantum computers.

The holy grail of studies on quantum turbulence is to understand and explain turbulence in classical fluids, according to the researchers, and this new work provides an initial step towards coming to grips with the inner workings of vortices in superfluids. From there, the researchers say, we could move on to comprehending turbulence in our everyday environment, in a “classic” state.

The implications, according to Makinen and Eltsov, could spin entire industries around, improving the aerodynamics of planes and vehicles of all kinds, for example, or controlling the flow of oil or gas in pipelines.