Shot noise measurements with an impedance matching circuit at GHz frequencies

Abstract

In this work, we present carbon nanotube (CNT) single and double quantum dots coupled to a GHz superconducting impedance matching circuit using a CNT stamping technique. The device shows a tunable bipolar double dot behavior, reaching the few-electron/hole regime. The resonance response reflected by the matching circuit is a sensitive probe of the charge state of the device, allowing a determination of the absolute charge number. The impedance matching circuit allows excellent shot noise measurement performance in a carbon nanotube single quantum dot regime. The signal to noise ratio at a device resistance of 100 kΩ is enhanced by a factor of 3.5 compared to a wide-band detection without impedance matching. We also perform shot noise measurements in ultra-clean graphene p-n junctions with an impedance matching circuit.