Electron localization in double quantum dots: ideal and realistic confinements

The two-level system theory is applicable for various quantum systems, such as bi-atomic molecules or double quantum dots (DQDs). The electron confinement in DQD is studied in different physical aspects. In this work, we discuss the electron localization in DQD in relation to symmetry breaking. Recently, we have shown [1] that the spectral distribution of electron localizations in DQDs strongly depends on the symmetry of the quantum dot confinements. The ideal symmetry means that the QD geometry and other physical parameters of the electron confinement in each QD are the same, but ideal DQD system cannot be experimentally produced. We modeled numerically both cases of confinement in InAs/GaAs DQD using single sub-band effective mass approach. Our model includes an effective potential, simulating the strain in the heterostructure, in the Schrödinger equation, which is solved by finite element method. The spectral distributions of localized/delocalized states are calculated. We show the effect of the realistic confinement on the electron localization in DQD in relation to the geometry and material mixing of the left/right symmetry violation. We also show that the electron localization in ideal DQD is unstable for any symmetry violation. The results lend themselves to discuss the widely used concept of "quantum dot molecules".