Modeling the level structure of a double quantum dot in the two-electron regime

We investigate a new type of multiphoton resonance in a four-level quantum system, where two of its levels are coupled strongly with two symmetric driving fields. Near the resonance condition where transitions occur, the different behaviors of the number of even and odd photons, n, is found to be consistent with experimental observations. By making all levels time-dependent, we compute the transition rates with resonant features. We explain this phenomenon in terms of groups of certain interfering trajectories of the multilevel systems, so that the behavior is insensitive to fluctuations of the energy of the driven levels, and survives deeply into the strong dephasing regime. Multiphoton resonances occur for the first time at the third order and for the second time at the fourth order of couplings and likewise for other higher orders. This study can be related to a variety of nanoscale solid state, atomic or molecular systems. An effective mechanism to explain previously implemented experiments in strongly driven double quantum dots is presented. (paper)