© Chien Liu and Lene V. Hau.
A light pulse slows and, at the same time, spatially compresses in a Bose-Einstein condensate. As a matter of fact, the pulse compresses by the same factor as it slows down. The light pulse also creates a holographic imprint in the condensate, and that little imprint follows along as the pulse slowly propagates through the atom cloud. When the light pulse exits the condensate, it accelerates back up and stretches out again to regain the length it had before it entered the atom cloud.