▎ 摘　　要

To get a carbon-based qubit, we pay attention to a triangular graphene quantum dot with two electrons occupying the degenerate shell. The spin of the dot is determined by the energy difference between the lowest spin-singlet and spin-triplet states. The energy difference is analyzed as a function of the dot size and an applied electric field. For different sizes, the curves of the energy difference share a similar outline: a brief oscillation as the initial party and a single big peak as the main party. Based on the obtained results, we analyze the spin switches controlled by the weak electric field, as well as by the strong electric field. The weak and strong electric fields have their own advantages in controlling spin switches. When the weak electric field is used for controlling spin switches, the graphene quantum dot with the larger size is available as a qubit. Our findings can be helpful for using a graphene quantum dot as a qubit.