Noise reduction by bias cooling in gated Si/Si$_x$ Ge$_{1−x}$ quantum dots

Silicon–germanium heterostructures are a promising quantum circuit platform, but crucial aspects, such 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 Al2 O 3 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 lHz
to 10 mHz. We measure the total noise power as a function of the applied voltage during cooldown in four different devices and find a mini-
mum in noise at 0.7 V 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