A radio-frequency (rf) matching circuit with an in situ tunable varactordiode used for rf reflectometry measurements in semiconductor nanostructures isinvestigated and used to optimize the sample-specific chip design. The samplesare integrated in a 2-4 GHz stub-matching circuit consisting of a waveguidestub shunted to the terminated coplanar waveguide. Several quantum pointcontacts fabricated on a GaAs/AlGaAs heterostructure with different chipdesigns are compared. We show that the change of the reflection coefficient fora fixed change in the quantum point contact conductance can be enhanced by afactor of 3 compared to conventional designs by a suitable electrode geometry.
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