Tunable ground-state degeneracies in double quantum dots

We have studied the effect of electron-electron interactions on planar double quantum dots subjected to an external magnetic field. Contrary to all other earlier works on similar systems, our accurate results for the energy levels and the dipole-allowed transition energies reveal the absence of singlet-triplet crossing (due to electron correlations only) in the case when the dots occupy only two electrons. For a larger number of electrons, we find the expected crossing of the energy levels. The corresponding far-infrared optical absorption spectra show the effect of electronic interactions as well as the underlying symmetries of these systems. The hyper-exponential increase of the exchange energy, as derived in our model, would facilitate the coherent control of the spin states in a double dot, as proposed in recent experiments.