A high speed radio-frequency quantum point contact charge detector for time resolved readout applications of spin qubits

In this paper, we give details related to the implementation of a rf-QPC charge detector coupled to a GaAs/AlGaAs triple dot. Each component of the readout circuit is discussed with emphasis on the isolator. We use a 10 K noise temperature HEMT amplifier in the readout and determine that the attenuation of amplifier noise that the isolator provides is not significant. A base electron temperature of 100 mK is reached independent of the existence of the isolator in the readout circuit. We also discuss the use of normal metal and superconducting resonant circuits. Using the superconducting resonant circuit, we detect charge motion in the device and determine that the bandwidth of the readout is at least 1 MHz with a sensitivity of 1.46×10‐4e/Hz.