  Excitonic systems localized in a single InAs/GaAs parabolic quantum dot are
studied theoretically using an unrestricted Hartree-Fock method. The binding
energies of excitons, conventional biexcitons and quadrons - four particles
system of two electrons and two holes, in the ground state have been obtained
as functions of magnetic field and confinement potential. It is found that for
strong confinement, while the binding energy of biexciton is negative, the
binding energy of quadron is positive, suggesting the strong lateral
confinement of the parabolic quantum dot supports the formation of a quadron
rather than a biexciton.
