SCL's Antun Balaz presented a seminar:

"Nonlinear Excitations in Bose-Einstein Condensates: Faraday Waves"

Abstract: 
In addition to collective oscillation modes, Bose-Einstein Condensates (BECs) exhibit a number of other excitations due to their inherent nonlinearity. Faraday (density) waves can be generated by a periodic modulation of the trapping potential or atomic interactions, and were first observed experimentally in 2007. Using the results of extensive numerical simulations and analytical variational calculations, we will show that elongated binary non-miscible BECs subject to periodic modulations of the radial confinement exhibit a Faraday instability similar to that seen in one-component condensates. Considering the hyperfine states of 87Rb condensates, we will show that there are two experimentally relevant stationary state configurations: the one in which the components form a dark-bright symbiotic pair (the ground state of the system), and the one in which the components are segregated (first excited state). 

For each of these two configurations, we will numerically demonstrate that far from resonances the Faraday waves excited in the two BEC components are of similar periods, emerge simultaneously, and do not impact the dynamics of the bulk of the condensate. We will also analytically derive the period of the Faraday waves using a variational treatment of the coupled Gross-Pitaevskii equations combined with a Mathieu-type analysis for the selection mechanism of the excited waves. Finally, we will show that for a modulation frequency close to twice that of the radial trapping, the emergent surface waves fade out in favor of a forceful collective mode that turns the two BEC components miscible.