Radio-frequency circuits are a powerful tool to perform fast and sensitive measurements on quantum devices . In the first part of this talk, I will focus on how we optimize this tool for readout of some of the most promising qubits in the solid-state. Sensitive measurements of these quantum devices are essential for high-fidelity single-shot qubit readout, but are hindered by poor impedance matching to the device. I will show how we achieved controllable perfect matching with a high device impedance ; a gate-defined GaAs quantum dot . Voltage-controlled capacitors allow in situ tuning of the matching condition, even accounting for parasitics, and enable an absolute calibration of the capacitance sensitivity. I will benchmark the results against the requirements for single-shot qubit readout using quantum capacitance. I will also show how radio-frequency circuits provides a new insight on the tunnelling processes occurring in a quantum dot.
In the second part of the talk, I will focus on measurements of motion. A radio frequency circuit allowed us to probe the vibrations of a suspended carbon nanotube . By using a gate voltage to tune the carbon nanotube into resonance with the radio-frequency signal, the mechanical signal is transduced efficiently to an electrical signal. I will evaluate the suitability of this readout scheme for monitoring mechanical motion at the level of uncertainty necessitated by the Heisenberg uncertainty principle.
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 “Sensitive radio-frequency measurements of a quantum dot by tuning to perfect impedance matching”, N. Ares et al., Phys. Rev. Applied *5*, 34011 (2016).
 “Resonant optomechanics with a vibrating carbon nanotube and a radio-frequency cavity”, N. Ares et al., Phys. Rev. Lett. *117*, 170801 (2016).