Thefeaturesofthelow-lyingspectraoffour-bodyA+B-A+B-systemshavebeendeducedbasedonsymmetry.Usingthemethodoffew-bodyphysics,wecalculatetheenergyspectraofA+B-A+B-systemsinaharmonicquantumdot.Wefindthatthebiexcitoninatwo-dimensionalquantumdotmayhaveotherboundexcitedstatesandthequantummechanicalsymmetryplaysacrucialroleindeterminingtheenergylevelsandstructuresofthelow-lyingstates.
