Scientists from the University of Tokyo and the National Institute of Standards and Technology in Gaithersburg, Md., have reported that a small number of atoms in a high-finesse microcavity can control the propagation of light pulses. Previous research had demonstrated that dense atomic media could slow or stop light as well as lead to the appearance of superluminal phenomena, but the team has proved that the same holds true for very few atoms. The scientists produced delays as high as 440 ns and advances as high as 170 ns in laser pulses that passed through clusters of fewer than 10 ⁸⁵Rb atoms in a magneto-optical trap of six circularly polarized laser beams. A description of the work appeared in the Dec. 2 issue of Physical Review Letters.