An international team of scientists created and observed a completely new type of vortex – whirling masses of fluid or air. The new paper details the first laboratory studies of these ‘exotic’ whirlpools in an ultracold gas of atoms at temperatures as low as tens of billionths of a degree above absolute zero, led by researchers from Amherst College in the United States and the Universities of East Anglia and Lancaster University in the United Kingdom.
The discovery, which was published this week in the journal Nature Communications, has exciting future implications for quantum information and computing implementations. From whirlpools of water down a bathtub drain to the airflow around a hurricane, vortices are common in nature.
In quantum-mechanical systems, such as an atomic Bose-Einstein condensate, vortices are typically tiny, and their circulation occurs in discrete, quantized units. Such vortices have long piqued the interest of physicists, and they have helped to shed light on the unusual properties of superfluidity and superconductivity.
The mass flow and the underlying symmetry of the fluid interact with one another in interesting ways. One consequence is that if the positions of two vortices are interchanged, they can leave a trace of the process lingering in the fluid. This trace links the interacting vortices together permanently, like a rung in a ladder.Dr. Magnus Borgh
The unusual nature of the observed whirlpools, on the other hand, is due to symmetries in the quantum gas. The appearance of asymmetric worlds despite perfect underlying symmetries is an especially fascinating property of physical theories ranging from cosmology to elementary particles. When water freezes to ice, for example, disordered molecules in a liquid arrange themselves into a periodic array.
The spatial symmetry of a system is often readily identified – for example, a honeycomb has a periodic array of cells with hexagonal symmetry. Although the vortex medium used in this new work is a fluid rather than a solid array, it also possesses an internal set of hidden discrete symmetries. For example, one of the team’s ultracold gases had the fourfold symmetry of a square, and another had the tetrahedral symmetry of a four-sided die, familiar to players of fantasy games everywhere.
“The mass flow and the underlying symmetry of the fluid interact with one another in interesting ways,” said Dr. Magnus Borgh, Associate Professor in Physics at UEA. “One consequence is that if the positions of two vortices are interchanged, they can leave a trace of the process lingering in the fluid. This trace links the interacting vortices together permanently, like a rung in a ladder.”
“No ordinary fluids behave like this, and it’s possible that analogous objects only exist deep inside neutron stars,” said Prof Janne Ruostekoski of Lancaster University. Indeed, the team claims that the vortices they created are above and beyond the state-of-the-art. “It’s partly these connections to strange domains of physics that make our work appealing,” said Prof David Hall of Amherst College. “It’s also due to our human appreciation for symmetry.”
Direct observation of these behaviors has become the focus of the team’s research, with the experimental portion based at Amherst College. “We’re fortunate to have extremely talented and dedicated students who can do these kinds of challenging experiments,” Prof Hall said, praising lead author Arthur Xiao in particular.