  The interaction of an ensemble of atoms with common vacuum modes may lead to
an enhanced emission into these modes. This phenomenon, known as superradiance,
highlights the coherent nature of spontaneous emission, resulting in
macroscopic entangled states in mundane situations. The complexity of the
typical observations of superradiance, however, masks its quantum nature,
allowing alternative classical interpretations. Here we stress how this picture
changed with the implementation ten years ago of a new process for
single-photon generation from atomic ensembles. We present then the last piece
of evidence for the superradiant nature of such process, reporting the
observation of an accelerated emission of the photon with a rate that may be
tuned by controllably changing the number of atoms in the ensemble. Such
investigation paves the way to a new, bottom-up approach to the study of
superradiance.
