Undoped accumulation-mode Si/SiGe quantum dots
  We report on a quantum dot device design that combines the low disorder properties of undoped SiGe heterostructure materials with an overlapping gate stack in which each electrostatic gate has a dominant and unique function -- control of individual quantum dot occupancies and of lateral tunneling into and between dots. Control of the tunneling rate between a dot and an electron bath is demonstrated over more than nine orders of magnitude and independently confirmed by direct measurement within the bandwidth of our amplifiers. The inter-dot tunnel coupling at the (0,2)<-->(1,1) charge configuration anti-crossing is directly measured to quantify the control of a single inter-dot tunnel barrier gate. A simple exponential dependence is sufficient to describe each of these tunneling processes as a function of the controlling gate voltage. 
Matthew G. Borselli, Kevin Eng, Richard S. Ross, Thomas M. Hazard,   Kevin S. Holabird, Biqin Huang, Andrey A. Kiselev, Pete...
cond-mat.mes-hall