Effect of Zeeman field on Kármán vortex street in spin-1 Bose–Einstein condensates

The dynamics of three-component spin-1 BEC with a moving obstacle in a uniform Zeeman field are numerically investigated. Four vortex patterns are observed in all three components: stable laminar flow, vortex pairs, Kármán vortex street and irregular vortex. We focus on the effect of Zeeman field on vortex street. It is found that enhancement of the quadratic Zeeman effect would lead to decrease in the parameter region generating vortex streets and inhibit the generation of vortex streets. When quadratic Zeeman effect increases, the generation of vortex street requires larger obstacle diameter and velocity. In addition, it is interesting to note that the size of vortex decreases gradually with the increase in quadratic Zeeman effect. The drag force acting on the obstacles is calculated, and the mechanical mechanism for various vortex patterns is analyzed. Finally, an experimental protocol for the above realization and observation is provided.