Kármán Vortex Street In A Two-component Bose-Einstein Condensate

The vortex of fluid is a kind of universal flow phenomenon in nature.When the fluid flows through some objects under certain conditions,the two rows of vortices with opposite rotation and regular arrangement,known as the Kármán vortex street,will be pe-riodically shed from both sides of the objects.Looking for this pattern of vortex shedding in superfluid is one way physicists can gain a deeper understanding of the relationship be-tween classical and quantum fluid.Bose-Einstein condensate,the precious macroscopic quantum phenomenon in physics,is a occupation of the same quantum state by all atoms when the temperature of system is less than a certain critical value.Since it was predict-ed theoretically in 1925 and realized experimentally in 1995,Bose-Einstein condensate provides a clean and well-controlled research ground for studying the quantized vortex in superfluid.Two-component Bose-Einstein condensate shows a variety of novel quantum phenomena because of the intra-and inter-component interaction.The study of quantum Kármán vortex street in a two-component Bose-Einstein condensate is of great value and significance.By numerical simulations based on the coupled Gross-Pitaevskii equations,the vor-tex shedding from a moving Gaussian obstacle potential in two-component Bose-Einstein condensates with different states,especially the quantum Kármán vortex street,is inves-tigated theoretically.The results of research show that:in a miscible two-component condensate composed of ²³Na and ⁸⁷Rb atoms,the Kármán vortex street composed of quantized vortices is formed in one component,while the density peak street composed of density peaks is formed correspondingly in the other component,and the half-quantum vortex street with composite vortex structure is composed of them;in an immiscible two-component condensate composed of the hyperfine states|F=1,mf=-1 and|F=2,mf=+1 of⁸⁷Rb atoms,the Kármán vortex street composed of quantized vortices is formed in one component,while the ghost vortex street composed of ghost vortices is formed concomitantly in the other component;the other typical patterns of vortex shedding,such as vortex dipoles and V-shaped vortex pairs,can also be formed in two-component condensates with different states,and the various vortex shedding patterns are related to the width and velocity of moving obstacle potential,especially the critical velocity is dependent on the width of obstacle potential.In addition,the results of calcu-lation show that the contribution to drag force acting on moving obstacle potential from vortex shedding.Finally,the corresponding experimental parameters for realization of the quantum Kármán vortex street in a two-component condensate and the further outlook on research prospect of related work are provided.