Playing quantum billiards with light and matter

October 13, 2015, Australian National University
Credit: ANU Polariton BEC laboratory.

An international team of physicists has created a quantum billiards game to gain new insights into the fundamental physics of exceptional points.

Researchers from ANU, Japan, Singapore and Germany, have for the first time demonstrated exceptional points in a large-scale quantum system using a Bose-Einstein condensate of exciton-polaritons.

The research opens a new direction in exciton-polariton physics and could lead to the discovery of new operating principles for future polariton-based electronics.

"Exceptional points signify interesting and counter-intuitive phenomena, such as unexpected transparency of opaque materials, unidirectional propagation of light, or lasers that shut down when you pump them harder," said team leader Dr Elena Ostrovskaya, from the ANU Research School of Physics and Engineering.

An exceptional point happens when two different states of a physical system coalesce into one. They have been predicted for quantum systems, but so far observed only with classical optical waves or microwaves.

Exciton-polaritons are hybrids of light and matter. Massive numbers of exciton-polaritons can behave in unison forming a giant quantum matter wave—a Bose-Einstein condensate.

By shining laser light into a piece of semiconductor, the research team made a billiard game measuring approximately 10 micrometers across.

They discovered that exciton-polaritons, used in this billiard game instead of billiard balls, exhibit abundant exceptional points in their spectrum.

The team used a quirky property of exceptional points in order to detect them. By going in a loop around the exceptional point in the parameter plane, you can never return to the same quantum state you started from. A second loop will then flip the state upside down.

This feature is called a topological Berry phase, and is exclusive to systems with exceptional points.

Explore further: Spiral laser beam creates quantum whirlpool

More information: T. Gao et al. "Observation of non-Hermitian degeneracies in a chaotic exciton-polariton billiard," Nature (2015). DOI: 10.1038/nature15522

Related Stories

Spiral laser beam creates quantum whirlpool

November 17, 2014

( —Physicists at Australian National University have engineered a spiral laser beam and used it to create a whirlpool of hybrid light-matter particles called polaritons.

New way to cool micro-electronic devices

May 18, 2015

(—A team of researchers working at the University of Grenoble has developed a new way to cool solids at the micro level. In their paper published in Physical Review Letters, the team describes how they used laser ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

Physicists reveal why matter dominates universe

March 21, 2019

Physicists in the College of Arts and Sciences at Syracuse University have confirmed that matter and antimatter decay differently for elementary particles containing charmed quarks.

ATLAS experiment observes light scattering off light

March 20, 2019

Light-by-light scattering is a very rare phenomenon in which two photons interact, producing another pair of photons. This process was among the earliest predictions of quantum electrodynamics (QED), the quantum theory of ...

How heavy elements come about in the universe

March 19, 2019

Heavy elements are produced during stellar explosion or on the surfaces of neutron stars through the capture of hydrogen nuclei (protons). This occurs at extremely high temperatures, but at relatively low energies. An international ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.