Enhanced tunnel conductance due to QCA cotunneling processes observed for silicon serial triple quantum dots

We study single-electron tunneling characteristics of silicon serial triple quantum dots which consist of lithographically-defined double quantum dots interconnected with a naturally-formed and smaller quantum dot. By controlling the single-electron tunneling through the triple quantum dots electrostatically using multiple side gates, the charge stability diagrams are characterized experimentally and theoretically. Several charge quadruple points are observed where sequential tunneling throughout the triple quantum dots is enabled. In addition, enhancement of tunnel conductance is observed along the two-hold degeneracy boundaries across which two electrons exhibit quantum cellular automata (QCA) cotunneling processes.