Charge detection of a quantum dot under different tunneling barrier symmetries and bias voltages

TL;DR

This study demonstrates how the symmetry of tunneling barriers in a coupled quantum dot system affects charge detection sensitivity, highlighting the importance of barrier symmetry in quantum dot sensor design.

Contribution

It provides experimental insights into the impact of tunneling barrier asymmetry on charge detection in coupled quantum dots, emphasizing the role of barrier symmetry in device performance.

Findings

Complete Coulomb diamonds observed with symmetric barriers

Detection signals depend on tunneling rate ratios

Transport involving excited states visible only with symmetric barriers

Abstract

We report on the realization of a coupled quantum dot (QD) system containing two single QDs made in two adjacent InAs nanowires. One QD (sensor QD) is used as a charge sensor to detect the charge state transition in the other QD (target QD). We investigate the effect of the tunneling barrier asymmetry of the target QD on the detection visibility of charge state transition in the target QD. The charge stability diagrams of the target QD under different configurations of barrier-gate voltages are simultaneously measured via the direct signals of electron transport through the target QD and via the detection signals of charge state transition in the target QD from the sensor QD. We find that the complete Coulomb diamond boundaries of the target QD and the transport processes involving the excited states in the target QD can be observed in the transconductance signals of the sensor QD only when the tunneling barriers of the target QD are nearly symmetric. These phenomena are explained by analyzing the effect of the ratio of the two tunneling rates on the electron transport processes through the target QD. Our results imply that it is important to consider the symmetry of the tunneling couplings when constructing a charge sensor integrated QD device or qubit.