“When the photon exits the medium, its identity is preserved,” Lukin said. “It’s the same effect we see with refraction of light in a water glass. The light enters the water, it hands off part of its energy to the medium, and inside it exists as light and matter coupled together, but when it exits, it’s still light. The process that takes place is the same it’s just a bit more extreme — the light is slowed considerably, and a lot more energy is given away than during refraction.” See: Seeing light in new light: Scientists create never-before-seen form of matter