Interference patterns in spiral wave drift induced by a two-point feedback.

The drift velocity field describing spiral wave motion in an excitable medium subjected to a two-point feedback control is derived and analyzed. Although for a small distance between the two measuring points a discrete set of circular shaped attractors are observed, an increase of induces a sequence of global bifurcations that destroy this attractor structure. These bifurcations result in the appearance of smooth unrestricted lines with zero drift velocity, similarly to zero intensity lines under destructive interference in linear optics. The existence of such unusual equilibrium manifolds is demonstrated analytically and confirmed by computations with the Oregonator model as well as by experiments with the light-sensitive Belousov-Zhabotinsky reaction.