Structure of binaryBose-Einstein condensates

Abstract

We identify all possible classes of solutions for two-componentBose-Einstein condensates (BECs) within the Thomas-Fermi (TF)approximation and check these results against numerical simulationsof the coupled Gross-Pitaevskii equations (GPEs). We find that theycan be divided into two general categories. The first class containssolutions with a region of overlap between the components. The otherclass consists of non-overlapping wavefunctions and also containssolutions that do not possess the symmetry of the trap. The chemicalpotential and average energy can be found for both classes within theTF approximation by solving a set of coupled algebraic equationsrepresenting the normalization conditions for each component. Aground state minimizing the energy (within both classes of states)is found for a given set of parameters characterizing the scatteringlength and confining potential. In the TF approximation, the groundstate always shares the symmetry of the trap. However, a fullnumerical solution of the coupled GPEs, incorporating the kineticenergy of the BEC atoms, can sometimes select a broken-symmetry stateas the ground state of the system. We also investigate effects offinite-range interactions on the structure of the ground state.