Rather than having photons of light roaming freely about, these researchers are able to (theoretically) control light so that it stays put in one place. The team of Andrew Greentree, Jared Cole, and Lloyd Hollenberg, of the School of Physics at the University of Melbourne, and Charles Tahan, of the University of Cambridge, have shown how to theoretically engineer a phase transition in photons of light.

Therefore, photons go from flowing freely (an initial state in which they do not interact with each other) to being fixed in a crystal-like state (a final state in which they do interact with each other, in fact, they repel each other).

A phase transition, in the field of thermodynamics, is a transformation (change) of a system from one phase to another phase, which is characterized by an abrupt transition in physical properties, for example, with water turning from liquid to ice (solid).

What a solid light phase transition means to technology, according to Greentree, is that, for instance, computers with the use of controlled photons of light can be made to solve extremely difficult problems in quantum physics—what today’s computers are too slow to accomplish. Generally, the discovery opens up a brand new realm of technical possibilities in science and engineering.

The team has not yet made a solid light device but are proposing to construct one using defects in the crystal lattice of thin sheets of diamonds. The system, if it works, would have quantum bits, or qubits, which could be used to make calculations. They feel that within a few years, using existing technology, their idea could be made into a quantum computer made of diamonds.

The work of the Universities of Melbourne and Cambridge team of Greentree, Cole, Hollenberg, and Tahan has been published in Nature Physics (“Quantum phase transitions of light”, December 1, 2006, pages 856-861) and New Scientist (“Engaging photons in light conversation, January 11, 2007).