This is really bizarre. (Some re-paragraphing ahead.)
"Most of the properties of light we know about originate from the fact that photons are massless, and that they do not interact with each other," Lukin said. "What we have done is create a special type of medium in which photons interact with each other so strongly that they begin to act as though they have mass, and they bind together to form molecules. This type of photonic bound state has been discussed theoretically for quite a while, but until now it hadn't been observed.I can't believe they did this. It's both bizarre and intriguing. And it's yet another reminder that we are an infant race, just discovering the nature of the world around us. And yet we think we know it all and have the right to ruin the planet for future generations. We know next to nothing.
Lukin also suggested that the system might one day even be used to create complex three-dimensional structures – such as crystals – wholly out of light.
"What it will be useful for we don't know yet, but it's a new state of matter, so we are hopeful that new applications may emerge as we continue to investigate these photonic molecules' properties," he said.