Capacitively coupled quantum dots as a single-electron switch

A double quantum dot in a GaAs/AlGaAs heterostructure with strong interdot capacitance but no interdot tunneling can be constructed using a floating metal gate that covers both dots and an etched trench between the dots that prevents tunneling. The interdot capacitance CINT=0.34CΣ between Dots 1 and 2, measured using the Coulomb blockade, was significantly larger than that measured for similar dots without a floating gate. When a single electron is added to Dot 1 the charge couples to Dot 2, and vice versa, causing the Coulomb blockade peaks to split. The change in dot conductance from peak splitting can be as large as two orders of magnitude, allowing the double dot to be used as a single-electron switch. The split conductance peaks observed for weak tunneling from each dot to its leads were fit by a thermally broadened line shape, and good agreement with the data was found. Charge fluctuations induced by stronger tunneling from Dot 2 to its leads softened the splitting transition on Dot 1 that was maintained in the weak tunneling regime. Under the same conditions the splitting for Dot 2 remained sharp.