In their study, just published in the major journal Science, Bradley and colleagues observed never-before-seen negative temperature states of quantum vortices in an experiment.
"Despite being important for modern understanding of turbulent fluids, these states have never been observed in nature," he said.
"They contain significant energy, yet appear to be highly ordered, defying our usual notions of disorder in statistical mechanics."
He describes understanding fluid turbulence as a challenging problem.
"Despite a long history of study, the chaotic nature of turbulence has defied a deep understanding. So much so, that the need for a complete description has been recognised as one of the Clay Mathematics Institute's unsolved 'Millennium Problems'."
An interesting aspect of turbulence was that it had universal properties, meaning turbulent systems on a scale from microscopic to planetary lengths appear to share similar descriptions and characteristics.
Nobel Laureate Lars Onsager came up with a toy theory for two-dimensional turbulence in 1949. Simply put, it states that if you add enough energy to a 2D system, turbulence will result in the appearance of giant vortices – just like in the atmosphere of Jupiter.
However, his theory only directly applies to superfluids, where vortices rotated in discrete or quantum steps, and were almost particle-like.
Seventy years on, the Queensland-Otago collaboration observed Onsager's predictions.
Bradley said they utilised the high degree of control available in the Bose-Einstein condensation laboratory in Queensland's Centre of Excellence for Engineered Quantum Systems, using optical manipulation technology pioneered there.
They created a superfluid by cooling a gas of rubidium atoms down to nearly absolute zero temperature, and holding it in the focus of laser beams.
The optical techniques developed allow them to precisely stir vortices into the fluid – much like stirring milk into coffee.
Lead author Dr Tyler Neely, of Queensland, said the amazing thing was that the group achieved this with light and at such a small scale.
"The cores of the vortices created in our system are only about one-tenth of the diameter a human blood cell," he said.
One of the more bizarre aspects of Onsager's theory was that the more energy that was added to the system of vortices, the more concentrated the giant vortices became.
But if these vortices were considered as a gas of particles moving around inside the superfluid, vortex clusters then existed in absolutely negative temperature states, below absolute zero.
"This aspect is really weird," Neely said.
"Absolute negative temperature systems are sometimes described as 'hotter than hot' because they really want to give up their energy to any normal system at positive temperature. This also means that they are extremely fragile.
"Our study counters this intuition by showing that since the vortices are sufficiently isolated inside the superfluid, the negative-temperature vortex clusters can persist for nearly 10 seconds."
