In 1954 Robert Dicke predicted a remarkable phenomenon. Imagine a dense cloud of two-level atoms in an excited state that can radiatively decay. Because each atom typically decays independently of its neighbors, the cloud is a collection of incoherent emitters. But, he argued, if the atoms interact coherently, through the same optical field into which they emit their photons, they would spontaneously and collectively radiate coherent and highly polarized light—an effect Dicke named superradiance. 1
Nearly a half-century later, Bose–Einstein condensates began emerging as a new tool for exploring many-body physics. Thanks to the BEC’s long coherence times, its collective motion induced by an optical field can be monitored with exquisite precision. In 1999 Wolfgang Ketterle, David Pritchard, and their MIT colleagues asked whether the motion of the atoms in a BEC can alter their interactions with an optical field. After shining laser light on a cigar-shaped condensate, the group...
