Researchers from the universities of Melbourne and Cambridge have unveiled a new theory that shows light can behave like a solid.

“Solid light will help us build the technology of this century,” says research team member, University of Melbourne physicist Dr Andrew Greentree.

Dr Greentree and School of Physics colleagues Jared Cole and Professor Lloyd Hollenberg, with Dr Charles Tahan of the University of Cambridge, made their ‘solid light’ breakthrough by studying light with tools more commonly used to study matter.

“Solid light photons repel each other as electrons do. This means we can control photons, opening the door to new kinds of faster computers,” says Dr Greentree.

“Many real-world problems in quantum physics are too hard to solve with today’s computers. Our discovery shows how to replicate these hard problems in a system we can control and measure.”

He says photons of light do not normally interact with each other. In contrast, the electrons used by computers strongly repel each other.

The team has shown theoretically how to engineer a ‘phase transition’ in photons, leading them to change their state so that they do interact with each other.

Mr Cole describes a phase transition as a change in the state of something – “such as when water becomes ice”.

“Usually, photons flow freely, but in the right circumstances, they repel each other, and form a crystal.”

He says phase transitions are important in science and technology, but only the simplest examples are as yet understood.

Dr Greentree says the solid light phase transition effect ties together two very different areas of physics, optics and condensed matter “to create a whole new way of thinking”.

“It is very exciting for the University of Melbourne and its international collaborators to be leading the world in this new area,” he says.

The team’s work has been reported in Nature Physics and New Scientist.