ALP Seminar: The Rayleigh-Taylor instability in a binary quantum fluid

Instabilities, where initially small fluctuations seed the formation of large-scale structures, govern the dynamics in wide variety of fluid flows. The Rayleigh-Taylor instability (RTI) is an iconic example that leads to the development of mushroom-shaped incursions when immiscible fluids are accelerated into each other. RTI drives structure formation throughout science and engineering including table-top oil and water mixtures; supernova explosions; and inertial confinement fusion.  Despite its ubiquity, controlled laboratory RTI experiments are technically challenging. Here we report the experimental observation of RTI in an initial phase separated binary superfluid consisting of a two-component Bose-Einstein condensate of $\Na23$ atoms. We induce the RTI at the interface between these components using a magnetic gradient force (i.e. the Stern-Gerlach effect) to press the components together and observe the growth of mushroom-like structures. The interface becomes stable when the components are pulled apart, and we spectroscopically measure the dispersion relation of the "ripplon" interface modes.