Optimization of sample-chip design for stub-matched radio-frequency   reflectometry measurements
  A radio-frequency (rf) matching circuit with an in situ tunable varactor diode used for rf reflectometry measurements in semiconductor nanostructures is investigated and used to optimize the sample-specific chip design. The samples are integrated in a 2-4 GHz stub-matching circuit consisting of a waveguide stub shunted to the terminated coplanar waveguide. Several quantum point contacts fabricated on a GaAs/AlGaAs heterostructure with different chip designs are compared. We show that the change of the reflection coefficient for a fixed change in the quantum point contact conductance can be enhanced by a factor of 3 compared to conventional designs by a suitable electrode geometry. 
S. Hellm\"uller, M. Pikulski, T. M\"uller, B. K\"ung, G.   Puebla-Hellmann, A. Wallraff, M. Beck, K. Ensslin, T. Ihn
cond-mat.mes-hall