Fast detection of single-charge tunneling to a graphene quantum dot in a multi-level regime

In situ-tunable radio-frequency reflectometry is used for fast charge-detection measurements on a graphene single quantum dot. The variable capacitance of our special matching network both grants tunability and compensates for the large stray capacitance between the charge sensor's contacts and the doped silicon oxide backgate. To demonstrate the high detection bandwidth thus achieved, the rates for tunneling into and out of the dot through the same barrier are determined. Finally, an analytical model for calculating these rates in the multi-level tunneling regime is presented and found to correspond very well to our experimental observations. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4733613]