Magnetic control of spin switches in a graphene quantum dot and two-electron spin qubit

To get a magnetically controllable spin qubit based on carbon materials, we study the energy spectra of a triangular graphene quantum dot with two electrons occupying the degenerate shell. The total spin of the system can be either 0 or 1 and thus provides a possible realization for a spin qubit. The spin-phase diagrams are employed to show the evolution of the spin with the change of external magnetic and electric fields. The spin switches can be achieved by changing the magnetic field strength in the realistic range. In addition, from the perspective of manipulating spin qubits, we present some typical control models of spin switches. Our findings support the possibility to realize a carbon-based spin qubit controlled by an external magnetic field.