Visualization of vortex dynamics in quantum turbulence: from reconnections to Kelvin waves

Enrico Fonda

(Universidad de Nueva York)

If liquid helium is cooled below about 2.17K, the liquid becomes a quantum fluid known as helium II. The most important property of helium II is superfluidity: mass flow without viscous friction. 
Moreover vorticity in superfluids is constrained to line-like topological defects called quantized vortices. The evolution of a tangle of these vortices defines a state known as quantum turbulence. Quantum turbulence is in some ways similar to classical turbulence; for example, both show a Kolmogorov energy spectrum. However, many features of quantum turbulence, such as its velocity statistics, are distinct from classical flows. Moreover, because of the absence of viscosity, the dissipation mechanism in the zero-temperature limit must be different. Theories suggest excitation of Kelvin waves following reconnection of quantized vortices as the main dissipation mechanism. These helical waves have been recently visualized and characterized for the first time.