We have studied the electronic properties and optical absorption spectra of three different cases of donor centers, D 0 , D − and D 2− , which are subjected to a perpendicular magnetic field, using the exact diagonalization method. The energies of the lowest lying states are obtained as function of the applied magnetic field strength B and the distance ζ between the positive ion and the confinement xy-plane. Our calculations indicate that the positive ion induces transitions in the ground-state, which can be observed clearly in the absorption spectra, but as ζ → 0 the strength of the applied magnetic field needed for a transition to occur tends to infinity.

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We present a study of the electronic structure of two laterally coupled Gaussian quantum dots filled with two particles. The exact diagonalization method has been used in order to inspect the spatial correlations and examine the particular spin singlet-triplet configurations for different coupling degrees between quantum dots. The outcome of our research shows this structure to have highly modifiable properties promoting it as an interesting quantum device, showing the possible use of this states as a quantum bit gate.PACS numbers: 73.21. La, The growing significance of mesoscopic quantum dots (QDs) in the development of microelectronic devices attracts great attention, partly due to their promising technological utilization, but also due to their novel quantum properties. These two-dimensional nanostructures offer a high degree of flexibility in their manufacturing process giving as a result a very interesting combination of a highly controllable structure showing quantum effects. Recent advances in the manipulation of electrically defined QDs open a new line of investigation in coupled quantum dots (CQDs) and a very interesting chance for the realization of a solid state implementation of the basic components for quantum computing. The interest on CQDs in the field of quantum computing was brought over since Loss and DiVincenzo proposal 1 on the possibility of an implementation based on the spin states of coupled single-electron quantum dots. Recent studies and experiments 2,3,4,5,6 have proven the feasibility of using the spin degree of freedom in vertically and laterally coupled few-electron QDs as systems in which interactions can be electro-optically tuned and therefore they can potentially taken as candidates for performing quantum operations.It is the purpose of the present paper to present an accurate theoretical study focused on the electronic structure of the two-particle GDQD in the absence of a magnetic field. The exact diagonalization method 7 has been used in order to solve the interacting many-body system as it is a tool of proven reliability for few-particle problems 8 . Electron-electron correlation effects are studied for the different spin superposition states and for a variety of configurations, from a weakly interacting laterally coupled quantum dot molecule to a strongly overlapped situation. The choice of an anisotropic Gaussian confining potential makes it possible to describe a more realistic situation. 4 We will show that not only in vertically coupled QDs interactions can be tuned but also in lateral QDs this effect can be achieved; furthermore, this systems could actually be used as dynamically tunable two-level systems.As shown in our previous research 9 , the special behavior of a GDQD filled with two electrons makes it a very promising arrangement for the creation of a dynamically tunable quantum gate. As noted by previous research 4,5,10 , one of the most attractive setup among fewparticle lateral quantum dots is the two-electron case in which the singlet and triplet states can b...