  Dicke superradiance, i.e., the enhanced spontaneous emission of coherent
radiation, is often attributed to radiation emitted by synchronized dipoles
coherently oscillating in phase. At the same time, Dicke derived superradiance
assuming atoms in entangled Dicke states which do not display any dipole
moment. To shed light on this apparent paradox, we study the intensity
distribution arising from two identical two-level atoms prepared either in an
entangled Dicke state or in a separable atomic state with non-vanishing dipole
moment. We find that the two configurations produce similar far field intensity
patterns, however, stemming from fundamentally distinct types of coherence:
while in the second case the atoms display coherence among the individual
particles leading to Young-type interference as known from classical dipoles,
atoms in Dicke states possess collective coherence leading to enhanced
spontaneous emission. This demonstrates that the radiation generated by
synchronized dipoles and Dicke superradiance are fundamentally distinct
phenomena and have to be interpreted in different ways.
