Dual Shapiro steps and fundamental transconductance in dc driven Bloch transistor

Abstract

We propose a superconducting circuit based on the Bloch transistor, a quantum device consisting of two small-capacitance Josephson junctions connected in series and having a small island in between. This device is driven by two dc electrical sources controlling Josephson oscillations of frequency $f_J = 2e\overline{V_J}/h$, related to the average voltage $\overline{V_J}$ on the transistor, and Bloch oscillations of frequency $f_B = \overline{I_B}/2e$, related to the average current $\overline{I_B}$ injected into the transistor island. Due to the Bloch transistor properties, these two types of oscillations can mutually phase lock, i.e., $f_J = f_B$. This leads to formation of current steps on the current-voltage curve at $\overline{I}_B = 2ef_J$, which are similar to the dual Shapiro steps appearing at current $\overline{I}=2ef$ under microwave irradiation of frequency $f$. Moreover, transconductance $\overline{I_B}/\overline{V_J}$ takes the fundamental value of $1/R_Q$, where $R_Q = h/4e^2$ is the resistance quantum. The obtained results pave the way to the alternative quantum standard of resistance, based on the superconducting circuit and operating without applying strong magnetic field.