Strong electron-occupancy dependence of the lever arm in few-electron quantum dot systems

Abstract

We quantitatively investigated the variation of gate lever-arm (\(\alpha\)) in quantum dot (QD) systems, focusing on its dependence on electron occupancy. The values of \(\alpha\) were obtained from Coulomb diamond measurements in a single quantum dot (SQD) and from the analysis of bias triangles near triple points in a double quantum dot (DQD) under finite DC bias. Utilizing charge sensor (CS) enabled clear detection of charge transitions even at low electron occupancies, revealing that the \(\alpha\) increases substantially as the electron number decreases. For the SQD, \(\alpha\) increased from \(28 \text{meV}/\text{V}\) with six electrons to \(48 \text{meV}/\text{V}\) in the single-electron regime − nearly 70% relative change − indicating enhanced sensitivity of QD energy levels to gate voltages. The electrostatic potential simulations further support this observation by showing that stronger electrostatic confinement, which leads to smaller QD dimensions, reduces electron occupancy and improves the controllability of energy levels via gate tuning. These findings highlight the importance of precise \(\alpha\) estimation for controlling QD energy levels, with implications for potential applications in QD-based qubit manipulations and charge sensing in scalable quantum devices.