A transistor. In some embodiments, the transistor includes a first superconducting source-drain, a second superconducting source-drain, a graphene channel including at least a portion of a graphene sheet, and a conductive gate. The first superconducting source-drain, the second superconducting source-drain, and the graphene channel together form a Josephson junction having a critical current. The graphene channel forms a current path between the first superconducting source-drain and the second superconducting source-drain. The conductive gate is configured, upon application of a electric field across the conductive gate and the graphene channel by applying a voltage, to modify the critical current.