Into the dark state.

Visitors to Lene Hau's laboratory at Harvard University leave their shoes at the door. Dark state is neither light nor matter, nor a simple combination of non-interacting light and matter, says Ron Walsworth, who works on dark states at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. In a paper to be published in "Physical Review Letters," later this year, Jeff Kimble and his colleagues at California Institute of Technology in Pasadena have shown how the dark state provides an unprecedented means to control and use the quantum properties of light.