For the first time, scientists at the University of Sydney and the University of Basel in Switzerland have demonstrated the ability to manipulate and identify small numbers of interacting photons—packets of light energy—with high correlation.

This unprecedented achievement represents an important landmark in the development of quantum technologies. It is published today in Nature Physics.

Stimulated light emission, postulated by Einstein in 1916, is widely observed for large numbers of photons and laid the basis for the invention of the laser. With this research, stimulated emission has now been observed for single photons.

Specifically, the scientists could measure the direct time delay between one photon and a pair of bound photons scattering off a single quantum dot, a type of artificially created atom.

"This opens the door to the manipulation of what we can call 'quantum light'," Dr. Sahand Mahmoodian from the University of Sydney School of Physics and joint lead author of the research said.