Abstract

Dilute-gas Bose-Einstein condensates (BECs) are a prime tool for the investigation of matter wave dynamics. While most experiments to date have been done with trapped BECs where interatomic interactions play a prominent role, these systems can also be manipulated in the opposite regime. By coherently outcoupling atoms from a trapped BEC , a free-falling stream of matter waves can be generated, called an atom laser. While previous experiments with atom lasers have mainly focused on the divergence of coherence of these streams, here we present studies geared towards fluid flow investigations. We describe advanced experimental techniques, such as fluid flow tracing to follow the flow, and atom interferometric techniques to characterize differential potentials. As an application, we detail a set of experiments observing caustics in an accelerated flow, which relates these systems to the broad field of catastrophe theory. We compare images obtained with pulsed vs. continuous output coupling, and observe a geometric transition from attached fan-like features to detached bow shock-like features when the atom laser encounters a repulsive barrier. These experiments provide a first glimpse at a new generation of fluid flow experiments with BECs. This work is supported by NSF under grant number PHY -2207588 and by the Henry Luce Foundation in connection to the Clare Boothe Luce Professorship Program. Partial support provided by NSF grants DMS -1941489 and PHY -2137848.