Scientists from Skolkovo Institute of Science and Technology (Skoltech) and their collaborators from the United Kingdom, were able to produce a stable, giant vortex in interacting polariton condensates, successfully tackling a familiar challenge in quantized fluid dynamics.
The latest findings offer new possibilities for producing exclusively structured coherent light sources and studying many-body physics under special extreme conditions. The study was recently published in the Nature Communications journal.
In the field of fluid dynamics, a vortex can be described as a region in which a fluid revolves around a line (3D) or a point (2D). Individuals would have clearly observed this vortex in their sink or would have experienced one in the form of turbulence while flying.
Vortices also exist in the quantum world: that is, the flow of a quantum fluid can generate a zone in which the particles spin persistently around a certain point. The prototypical signature of these quantum vortices is their singular phase at the heart of the vortex.
Natalia Berloff and Pavlos Lagoudakis, both Skoltech Professors, and their collaborators investigated vortices produced by polaritons — unusual hybrid quantum particles that are half-matter (electrons) and half-light (photon) — creating a quantum fluid under the right conditions.
The researchers were searching for a way to produce vortices in these polariton fluids with high values of angular momentum (getting them to spin fast). Such vortices, also called giant vortices, are usually quite hard to achieve because they tend to split into several smaller vortices with low values of angular momentum in other systems.
The creation of stable giant vortices has shown that non-equilibrium (open) quantum systems, similar to polariton condensates, can resolve some extreme limitations of their thermodynamic equilibrium counterpart, like Bose-Einstein condensates of cold atoms.
Better control over the vorticity of a quantum fluid can provide new perspectives on analog simulation of the dynamics of black holes and gravity in the microscopic realm. The polariton condensate constantly produces photons that carry all the complexities of the vortex which could become significant for optical data storage, processing and distribution applications.
The investigators have been working on applying interacting polariton condensates as candidates to replicate a planar vector model, called the XY model. They observed that when numerous condensates were organized into the usual polygon with an odd number of vertices, the ground state of the entire system could match with a particle current along the polygon edge.
By moving from a triangle, pentagon, heptagon, etc., the team demonstrated that the current rotated increasingly faster, creating a giant vortex of different angular momentum.
The formation of stable clockwise, or anticlockwise, polariton currents along the perimeter of our polygons can be thought of as a result of geometric frustration between the condensates. The condensates interact like oscillators that want to be in antiphase with each other. But an odd-numbered polygon cannot satisfy this phase relation because of its rotational symmetry, and therefore the polaritons settle for the next-best thing which is a rotating current.
Tamsin Cookson, Study First Author, Skoltech
“This is a very nice demonstration of how polaritons can provide a very flexible sandbox to probe some of the more complex phenomena of nature. What we show here is a system that shares a lot of characteristics with a black hole, which still emitting, a white hole if you wish!” concluded Professor Lagoudakis.
The study also involved other organizations, like the University of Southampton, the University of Cambridge, and Cardiff University.
Cookson, T., et al. (2021) Geometric frustration in polygons of polariton condensates creating vortices of varying topological charge. Nature Communications. doi.org/10.1038/s41467-021-22121-3.