ANU physicists have made a spiral laser beam and it can be put to use in order to generate a whirpool of hybrid polaritons which are light-matter particles. “Creating circulating currents of polaritons – vortices – and controlling them has been a long-standing challenge,” said leader of the team, theoretician Dr Elena Ostrovskaya, from the Research School of Physics and Engineering.
“We can now create a circulating flow of these hybrid particles and sustain it for hours.”
Polaritons are the particles that posses the properties of both light and matter. The capability of controlling the flow of polaritons in this way can aid the development of completely novel technology to connect conventional electronics with new fiber and laser based technologies.
Polaritons are made in semiconductors when laser light interacts with the negatively charged electrons and positively charged holes in such a strong manner that it is not possible to distinguish the light from matter.
The team made the spiral beam by putting the laser through a piece of brass that has a spiral pattern of holes in it. This was directed into a semiconductor microcavity which is a tiny wafer of aluminum gallium arsendie which is a material used in LEDs, placed between two reflectors.
“The vortices have previously only appeared randomly, and always in pairs that swirl in opposite directions,” said Dr Robert Dall, who led the experimental part of the project.
“However, by using a spiral mask to structure our laser, we create a chiral system that prefers one flow direction. Therefore we can create a single, stable vortex at will.”
Such vortices are instances of quantum field behavior in which the polaritons coalesce into a special state of matter called the Bose-Einstien condensate.
“As well as being a window into the quantum world, these polaritonic vortices could be used to construct extremely sensitive detectors of electromagnetic fields, similar to SQUIDS (Superconducting QUantum Interference Devices),” Dr Ostrovskaya said.
“They could also be employed as quantum information carriers.”
The ANU team has pioneered the study of microcavity polaritons in Australia and hope their success will inspire other research groups around the country.
“Polaritonics is a rapidly developing research field all around the world. We hope we can build a network of groups researching these devices across Australia and joining the international effort,” Dr Ostrovskaya said.