Collective emission of matter-wave jets from driven Bose-Einstein condensates

Scattering is an elementary probe for matter and its interactions in all areas of physics. Ultracold atomic gases provide a powerful platform in which control over pair-wise interactions empowers us to investigate scattering in quantum many-body systems. Past experiments on colliding Bose-Einstein condensates have revealed many important features, including matter-wave interference, halos of scattered atoms, four-wave mixing, and correlations between counter-propagating pairs. However, a regime with strong stimulation of spontaneous collisions analogous to superradiance has proven elusive. Here we access that regime, finding that runaway stimulated collisions in condensates with modulated interaction strength cause the emission of matter-wave jets which resemble fireworks. Jets appear only above a threshold modulation amplitude and their correlations are invariant even as the ejected atom number grows exponentially. Hence, we show that the structures and occupations of the jets stem from the quantum fluctuations of the condensate. Our findings demonstrate the conditions for runaway stimulated collisions and reveal the quantum nature of the matter-wave emission.