Effect Of Discrete Intensities And Three-body Interactions In Continuous BEC On Kármán Vortex Street

The bosons will fall from the higher energy level to the lowest if the temperature is low enough.The state is called Bose-Einstein condensate(BEC for short).The realization of alkali atom BEC in 1995 provides a platform for further study.Due to the coherence of condensates,solitons and vortices in the system have become the focus of research.Under certain conditions,two regular lines of linear vortices appear when fluid flows through obstacles,and Karman vortex street is formed by nonlinear action.Three-body interaction can affect the stability of BEC,and a small strength of three-body interaction can also increase the number of atoms in condensate.The study for stability of BEC under two-and three-body interactions is helpful for future applications of ultracold gases.In addition,experimental techniques in optical lattices demonstrate the importance of discrete BEC systems.Important quantum phenomenas such as solitons and vortices can be observed in discrete BEC.At present,there are many researches on Kármán vortex street in continuous BEC,but few on discrete BEC.The study of Kármán vortex street in BEC is helpful for understanding the difference and relation between classical and quantum fluids.Based on this,the Gross-Pitaevskii(GP)equation is used to study the vortex shedding mode after the moving obstacle potential in a quasi-two-dimensional BEC with twoand three-body interactions in this paper.The effects of three-body interaction,the width and moving velocity of obstacle potential on vortex structure are analyzed in detail.By calculating the variation of distance and angular velocity between vortex pairs and the influence of drag force on obstacle potential,the physical mechanism of vortex generation is studied.The results of numerical simulation show that stable Karman vortex street phenomenon will appear in the system considering the three-body interaction when the two-body interaction is attractive or repulsive.The stability condition of Karman vortex street formation in BEC is less than that without considering the three-body interaction.Considering the three-body interaction,the larger velocity and smaller width of obstacle potential are more conducive to the formation of Karman vortex street.Finally,we provide schemes for realizing vortex street when the two-body interaction is attractive or repulsive in BEC with three-body interaction.In this paper,based on GP equation,the wave function of system is extended by Wannier function,and the discrete nonlinear Schrodinger equation can be obtained.Based on this equation,the vortex shedding pattern after moving obstacle potential in discrete quasi-two-dimensional BEC is studied.The results of numerical simulation show that four kinds of vortex structures are found under different discrete intensities.The stability conditions for the formation of Kármán vortex street in discrete BEC are less than those in continuous BEC,and with the increase of the discrete intensities,the stability conditions of vortex street are more similar to those in classical fluids.In addition,the density distribution in BEC will be changed with the increase of discrete intensities,and the area of vortex street is obviously narrower than that of other vortex types.When the moving speed of obstacle potential is accelerated,Karman vortex street will be formed more easily.