Fast single-charge sensing with a rf quantum point contact

We report high-bandwidth charge sensing measurements using a GaAs quantum point contact embedded in a radio frequency impedance matching circuit (rf-QPC). With the rf-QPC biased near pinch-off where it is most sensitive to charge, we demonstrate a conductance sensitivity of 5×10−6e2∕hHz−1∕2 with a bandwidth of 8MHz. Single-shot readout of a proximal few-electron double quantum dot is investigated in a mode where the rf-QPC back action is rapidly switched.