Study finds quantum state of spinning superfluid can discharge in three ways

According to a recent study from the University of Helsinki, published in the journal Physical Examination LettersA vortex of a superfluid quantized four times has three ways of splitting, depending on temperature.

The fluid transforms into a superfluid close to the absolute zero temperature point (around -273°C). Internal resistance forces, such as friction, disappear. At this stage, the behavior of the fluid can no longer be described by classical mechanics; rather, quantum physics must be applied.

When a superfluid is rotated, the resulting rotation should never slow down because superfluids have no viscosity or friction. This was experimented with at the atomic level using very slowly rotating helium, and it was observed that the superfluid eventually stopped.

The reason is that the vorticity of a superfluid becomes quantized: the overall vorticity breaks up into small vortices; angular momentum is both quantized and persistent and therefore does not disappear.

Rotation is restricted

A regular vortex, like water flowing out of a sink, can rotate on its axis at any speed, whereas the angular momentum of a quantized vortex is always proportional to an integer. This integer is called the winding number. The winding numbers of the individual and quadruply quantized vortices are one and four, respectively.

A quadruply quantized vortex easily splits into four once-quantized vortices, because a quadruply quantized vortex is more unstable due to the significant decrease in system energy after splitting. Lower energy means a more stable system.

Doctoral researcher Xin Li from the University of Helsinki studied quadruply quantized vortex splitting processes in his recent work. What happens when an unstable, quadruply quantized vortex can exist at three different temperatures, all still very close to absolute zero?

Three temperatures, three splitting modes

In the study, it was observed that the quadruply quantized vortices have three ways of splitting, leading to three different models. Although these patterns were theoretically identified in previous studies, the results demonstrated for the first time that temperature leads to different division processes.

The split was modeled by applying a relatively new theory to the phenomenon, known as gauge/gravity duality or holography. This duality allows for a systematic examination of the impact of temperature in a way that closely resembles a realistic situation.

The study indicates that there are two patterns observed in the low temperature range, while a third pattern may appear if the temperature rises further. Experimentally, two such division patterns have been observed so far, and the researchers suggest that at a higher temperature, a new pattern might become visible.