SCL's Antun Balaz presented a seminar:

"Nonlinear Excitations in Bose-Einstein Condensates: Parametric and Geometric Resonances"

Abstract:
Bose-Einstein Condensates (BECs) are inherently nonlinear quantum systems, which leads to a number of interesting effects. Modulation of some of the parameters of a BEC can give rise to prominent nonlinear features, such as shifts in the frequencies of collective oscillation modes, higher harmonics generation, and resonant mode coupling. In a recent experiment, a Bose-Einstein condensate of Li-7 has been excited by a harmonic modulation of the atomic s-wave scattering length. Combining an analytical perturbative approach with extensive numerical simulations, we will analyze the emerging nonlinear dynamics of the system on the mean-field level at zero temperature. We will present resulting excitation spectra and main nonlinear effects close to parametric resonances. We will also discuss geometric resonances in BECs with two-body and three-body contact interactions, where even a geometry of the trapping potential leads to the emergence of nonlinear effects, frequency shifts and resonant mode coupling.