Controlling dynamics in atom-optics billiards with external force fields

Summary form only given. We investigate classical dynamics of curved-trajectory billiards that would have been hyperbolic (i.e. billiards with non-vanishing Lyapunov exponent) if the particle had moved in straight lines. We introduce the curvature by applying external force fields on the particle. We analytically show that this can lead to the formation of elliptical orbits in hyperbolic billiards, and experimentally demonstrate these effects, using atom-optics billiards where ultracold atoms are trapped inside a dark optical trap, whose shape can be varied to create different atom dynamics.