Polariton filter coverts laser beam into quantum light

25 Feb 2019

Significant development led by Macquarie, Australia, could improve applications in quantum communication and optical quantum data processing.

An international team of researchers led by Macquarie University, Sydney, Australia, has demonstrated a new approach for converting what they call ordinary laser light into “genuine quantum light”.

The approach uses nanometer-thick films made of gallium arsenide, a semiconductor material widely used in solar cells. They sandwich the thin films between two mirrors to manipulate incoming photons.

The photons interact with electron-hole pairs in the semiconductor, forming new chimeric particles called polaritons that carry properties from both the photons and the electron-hole pairs. The polaritons decay after a few picoseconds, and the photons they release exhibit distinct quantum properties, known as signatures.

The team comments, “While these quantum signatures are weak at the moment, the work opens up a new avenue for producing single photons on demand.” The research has been published in Nature Materials.

Associate Professor Thomas Volz from Macquarie’s Department of Physics and Astronomy, and senior author on the paper, commented, “The ability to produce single photons on demand is hugely important for future applications in quantum communication and optical quantum information processing. Consider potential applications like unbreakable encryption, super-fast computers, more efficient computer chips or even optical transistors with minimal power consumption."

Exceeding current limitations

Currently single-photon emitters are typically created by materials engineering—where the material itself is assembled in such a way that the 'quantum' behaviour is built in. But this standard approach faces serious limitations at smaller and smaller scales because producing identical single-photon emitters by pure materials engineering is extremely challenging.

"This means our approach could be much more suitable for massively scaling up, once we can increase the strength of the quantum signatures we are producing. We might be able to make identical quantum emitters from semiconductors by photon nanostructure engineering, rather than by direct materials engineering," said Dr. Guillermo Munoz Matutano, also from Macquarie and lead author of the paper.

Dr Volz added, “While real-world applications are still a fair bit away, our paper describes a major milestone that the polariton community in particular has been waiting on for the last ten to fifteen years. The regime in which polaritons interact so strongly that they can imprint quantum signatures on photons has not been accessed to date and opens up a whole new playground for researchers in the field."