Australian Group Creates Sustained Polariton Whirlpool
Physicists at the Australian National University (ANU) have engineered a spiral laser beam and used it to create a whirlpool of hybrid light-matter particles called polaritons.
The team created the beam by putting their laser through a piece of brass with a spiral pattern of holes in it. This was directed into a semiconductor microcavity, a tiny wafer of AlGaAs, sandwiched between two reflectors.
"Creating circulating currents of polaritons - vortices - and controlling them has been a long-standing challenge," said leader of the team, theoretician 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 form in semiconductors when laser light interacts with electrons and holes so strongly that it is no longer possible to distinguish light from matter. The ability to control polariton flows in this way could aid the development of completely novel technology to link conventional electronics with new laser and fibre-based technologies.
"The vortices have previously only appeared randomly, and always in pairs that swirl in opposite directions," said Robert Dall, who led the experimental part of the project.
"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)," 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.
'Creation of Orbital Angular Momentum States with Chiral Polaritonic Lenses' by Dall et al, is published in Phys. Rev. Lett. 113, 200404.