Nature Phys. http://doi.org/brmp (2016)

Although the exact role that different quantum systems — photonic, solid-state and others — will play in large-scale quantum information processing is currently unclear, controlling atom–light interactions is likely to be crucial in devices such as quantum repeaters. Now, Jesse Everett and colleagues report the observation of self-stabilizing stationary light with a technique that might prove advantageous for applications in quantum information processing. The team uses the gradient echo memory method to create a spin wave (that is, a collective excitation) between two atomic levels in a cloud of cold rubidium atoms. Subsequently, two counter-propagating bright control fields illuminate the atomic ensemble in the presence of two weak probe beams so that the dynamics of the resulting atom–light interaction can be studied. Two photodetectors collect the output probe light, and the evolution of the spin wave is also captured through absorption imaging of an additional resonant field on a charge-coupled device (CCD) camera. Large signals at the detectors indicate that the atom–light system evolves to a stable configuration where a stationary optical field is trapped in the atomic cloud. The ability to precisely engineer the spatial profile of the spin wave lends flexibility to the scheme.