  We theoretically study biexcitons and quadrons in quantum dots with parabolic
confinement and give a complete comparison between the two excitations. The
calculation of quadron and biexciton binding energies as functions of
electron-to-hole confinement potentials and mass ratios, using unrestricted
Hartree-Fock method, shows the essential differences between biexciton and
quadron. The crossover between the negative and positive binding energies is
indicated. Besides, the effect of external magnetic field on the quadron and
biexciton binding energies has also been investigated. In addition, the
crossing between anti-binding and binding of both excited quadron and biexciton
states at a certain range of the electron-to-hole oscillator length ratios has
been found.
