Shot noise of a quantum dot measured with GHz stub impedance matching

TL;DR

This paper demonstrates GHz impedance matching using a stub tuner to measure shot noise in a quantum dot, significantly improving signal detection efficiency and enabling detailed noise analysis at high frequencies.

Contribution

It introduces a superconducting stub tuner for impedance matching in shot noise measurements of quantum dots, allowing accurate circuit parameter extraction and enhanced measurement sensitivity.

Findings

Signal to noise ratio improved by up to 800 times

Shot noise exhibits oscillating suppression and enhancement patterns

Impedance matching parameters reliably deduced from reflectance measurements

Abstract

The demand for a fast high-frequency read-out of high impedance devices, such as quantum dots, necessitates impedance matching. Here we use a resonant impedance matching circuit (a stub tuner) realized by on-chip superconducting transmission lines to measure the electronic shot noise of a carbon nanotube quantum dot at a frequency close to 3 GHz in an efficient way. As compared to wide-band detection without impedance matching, the signal to noise ratio can be enhanced by as much as a factor of 800 for a device with an impedance of 100 k$\Omega$. The advantage of the stub resonator concept is the ease with which the response of the circuit can be predicted, designed and fabricated. We further demonstrate that all relevant matching circuit parameters can reliably be deduced from power reflectance measurements and then used to predict the power transmission function from the device through the circuit. The shot noise of the carbon nanotube quantum dot in the Coulomb blockade regime shows an oscillating suppression below the Schottky value of $2eI$, as well an enhancement in specific regions.