Probing the non-linear dispersive response of a strongly driven quantum dot at gigahertz frequencies

Minimizing the number of physical gates required for control of semiconductor spin qubits is an important problem. A promising strategy is to use rf reflectometry with “gate-based” charge sensing for qubit readout. Studies to date have focused on charge sensing performance in the regime of weak rf driving where the response is linear, but when driven strongly the admittance of a quantum dot saturates to a constant ac current due to Coulomb blockade.

Here we present the results of an rf reflectometry experiment on a quantum dot patterned in silicon by scanning tunneling microscope lithography. The quantum dot is addressed by only one gate and one reservoir lead, specifically designed to maximize the nonlinearity of the admittance. We observe saturation of the response at high driving amplitudes and verify the response predicted by a simple rate equation model.

We study the performance of a quantum dot as a microwave mixer, demonstrating wide bandwidth down-conversion of signals 0-5 GHz. The quantum dot as an on-chip microwave mixer may be a useful tool for modulating qubit control signals in future solid-state quantum computing applications.