Measuring interactions between tunnel-coupled quantum dots

We report low-temperature tunneling measurements through double and triple quantum dots with adjustable interdot tunnel conductance, fabricated in a GaAs/Al_xGa_1-xAs heterostructure. As interdot tunnel conductance is increased, Coulomb blockade conductance peaks split into two peaks for double dots and three for triple dots. The splitting approaches zero for weak tunneling and saturates as the dots merge for strong tunneling. Coupled double and triple dots with different gate capacitance show quasiperiodic beating and peak suppression for weak interdot tunneling. Analysis of the data in terms of tunneling and classical charging theories shows that quantum charge fluctuations due to interdot tunneling dominate dot interactions when interdot tunnel conductance approaches 2e²/h.