Fluids governed by quantum mechanics’ strange rules have a particular restriction: a vortex in a quantum fluid can only twist by whole-number units. But while the smallest possible quantum vortex, with a single unit of rotation, has been seen in many systems, larger vortices are not stable.
While researchers have endeavored to constrain larger vortices to hold themselves together, the outcomes have been mixed: When the vortices formed, the severity of the methods utilized have generally destroyed their usefulness.
Now, scientists from the University of Cambridge have discovered a theoretical mechanism through which large quantum vortices can remain stable and form themselves in otherwise near-uniform fluids. This mechanism could help in experiments that might provide insight into the nature of rotating black holes with similarities with giant quantum vortices.
For this study, a quantum hybrid of light and matter called a polariton were used. When shining a laser light onto specially layered materials, these particles are formed.
Samuel Alperin and Professor Natalia Berloff from the University of Cambridge said, “When the light gets trapped in the layers, the light and the matter become inseparable, and it becomes more practical to look at the resulting substance as something distinct from either light or matter while inheriting properties of both.”
Alperin said, “The result is a fluid which is never allowed to settle, and which doesn’t need to obey what are usually basic restrictions in physics, like the conservation of energy. Here the energy can change as a part of the dynamics of the fluid.”
Scientists exploited the same constant flow of liquids light to allow the elusive giant vortex to form. Instead of shining the laser on the polariton fluid itself, the new proposal has the light shaped like a ring, causing a constant inward flow. According to the theory, this flow is enough to concentrate any rotation into a single giant vortex.
Alperin said, “That the giant vortex really can exist under conditions that are amenable to their study and technical use was quite surprising, but it just goes to show how utterly distinct the hydrodynamics of polaritons are from more well-studied quantum fluids. It’s exciting territory.”
Scientists noted, “They are just at the beginning of their work on giant quantum vortices. They simulated several quantum vortices’ collisions as they dance around each other with ever-increasing speed until they collide to form a single giant vortex analogous to black holes’ collisions. They also explained the instabilities that limit the maximum vortex size while exploring intricate physics of the vortex behavior.”
Alperin said, “These structures have some interesting acoustic properties: they have acoustic resonances that depend on their rotation, so they sort of sing information about themselves. Mathematically, it’s quite analogous to the way that rotating black holes radiate information about their properties.”
“The similarity could lead to new insights into the theory of quantum fluid dynamics, but they also say that polaritons might be a useful tool to study the behavior of black holes.”
- Samuel N. Alperin et al. Multiply charged vortex states of polariton condensates, Optica (2021). DOI: 10.1364/OPTICA.418377