Noise reduction by bias cooling in gated Si/SixGe1-x quantum dots

TL;DR

This study investigates how bias cooling voltage affects charge noise in silicon-germanium quantum dots, demonstrating a significant noise reduction and analyzing cooldown-to-cooldown variability to improve quantum device stability.

Contribution

It provides the first extensive quantitative analysis of bias cooling effects on charge noise in Si/SiGe quantum dots, including over 80 cooldowns and noise minimization strategies.

Findings

Optimal bias cooling voltage is around 0.7V for minimal noise.

Median noise power reduced by a factor of 6.

Cooldown-to-cooldown noise variation analyzed and characterized.

Abstract

Silicon-Germanium heterostructures are a promising quantum circuit platform, but crucial aspects as the long-term charge dynamics and cooldown-to-cooldown variations are still widely unexplored quantitatively. In this letter we present the results of an extensive bias cooling study performed on gated silicon-germanium quantum dots with an Al2O3-dielectric. Over 80 cooldowns were performed in the course of our investigations. The performance of the devices is assessed by low-frequency charge noise measurements in the band of 200 micro Hertz to 10 milli Hertz. We measure the total noise power as a function of the applied voltage during cooldown in four different devices and find a minimum in noise at 0.7V bias cooling voltage for all observed samples. We manage to decrease the total noise power median by a factor of 6 and compute a reduced tunneling current density using Schr\"odinger-Poisson simulations. Furthermore, we show the variation in noise from the same device in the course of eleven different cooldowns performed under the nominally same conditions.