Enhanced phase and charge diffusion due to radio-frequency/microwave excitation in Bloch transistors

Current-voltage characteristics and switching current of Bloch transistors under radio-frequency/microwave excitations were experimental studied, respectively revealing pronounced summational superconducting phase diffusion and central-island charge diffusion. The phase diffusion, which can be quantified by the zero-bias resistance, was found minimal when two charge states in the transistor are degenerate. The switching current, which also reflects the charge diffusion, was observed that becomes minimal at the degeneracy beyond a threshold in ac driving power. The charge diffusion was analyzed using an electric dipolar interaction between the photon field and excess charge on the central island