Tunable p–n junction barriers in few-electron bilayer graphene quantum dots

Abstract

Graphene quantum dots provide promising platforms for hosting spin, valley, or spin-valley qubits. Taking advantage of their electrically generated bandgap and their ambipolar nature, high-quality quantum dots can be defined in bilayer graphene using natural p–n junctions as tunnel barriers. In these devices, demonstrating the electrical tunability of the p–n junction barriers and understanding its physical mechanism, especially in the few-electron regime, are essential for further manipulating electrons' quantum degrees of freedom to encode qubits. Here, we show the electrostatic confinement of single quantum dots in bilayer graphene using natural p–n junctions. When the device is operated in the few-electron regime, the electron tunneling rate is found to be monotonically tuned by varying gate voltages, which can be well understood from the view of manipulating the p–n junction barriers. Our results provide an insightful understanding of electrostatic confinement using natural p–n junctions in bilayer graphene, which is beneficial for realizing graphene-based qubits.