Brass mask used to create spiral laser beam (Stuart Hay, ANU)Physics Technology 

Physicists Make a Quantum Whirlpool

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Imagine changing matter into light and light into matter, and then using that technology to build computers that are faster and more powerful than anything most of us can dream of.

That dream is closer to reality thanks to a new discovery that could link electronics with photonics. Physicists have successfully engineered a spiral laser beam that can create a vortex, or quantum whirlpool, of particles called polaritons, hybrid particles with the properties of both matter and light. Polaritons form in semiconductors when laser light interacts with electrons and holes (positively charged vacancies) so strongly that it is no longer possible to distinguish light from matter.

“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 at The Australian National University (ANU). “We can now create a circulating flow of these hybrid particles and sustain it for hours.”

The ability to control polariton flows could help link conventional electronics with new laser and fibre-based technologies, leading to amazing computing capabilities. “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.”

“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 team created the quantum whirlpool 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 aluminium gallium arsenide, a material used in LEDs, sandwiched between two reflectors.

The ANU team has pioneered the study of microcavity polaritons in Australia and hope their success will inspire other scientists to explore the possibilities of light and matter.

The study is published in the journal Physical Review Letters.

Image: Brass mask used to create spiral laser beam (Stuart Hay, ANU)

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