Evaluation of serially coupled triple quantum dots with a compact device structure by a simultaneous voltage-sweeping method

Series coupled triple quantum dots (TQDs) have been studied as an important element of quantum computers. It is needed to fabricate QD array connected in series with a compact structure to scale up the quantum bits. To develop quantum bits based on the TQDs, evaluation of the charge stability diagram is needed. However, since the center gate usually couples to all dots in the compact TQDs, it is difficult to achieve the charge stability diagram of TQDs by simply scanning the gate voltages. Here, we propose a simple method to achieve the stability diagram of TQDs. First, we check the stability diagram of the compact TQDs by the use of Monte Carlo simulations and succeed in developing a method to achieve the stability diagram by simultaneously sweeping of three gate voltages in the simulation. Then the method is applied to a silicon TQDs device fabricated by pattern-dependent oxidation. As the result, the formation of TQDs together with its stability diagram is confirmed.