First a light pulse is sent into the first condensate, where as expected, the light slows down. Then the coupling laser is turned off completely. The information is stored in the condensate and then strangely, a matter wave containing all of the light's information moves out of the first condensate into free space. It moves slowly to the second condensate. Then the control laser is illuminated and the original light pulse is emitted from the second condensate. This magic trick of light allows Hau to manipulate, or in another word process, the matter wave before it enters the second condensate.