Scalability of supercurrent modulable with single Cooper-pair transistors connected in parallel

Abstract

A single Cooper-pair transistor (SCPT) can work as a fast supercurrent switch. However, a direct combination of an SCPT with other superconducting-electronics circuits is not easy because of the smallness of the switchable supercurrent with it. In this work, scalability of the supercurrent that can be modulated with an SCPT structure is studied using multiple SCPTs connected in parallel having a common gate electrode. It is found that the magnitude of the maximum supercurrent is scaled up almost linearly with the increase in the number of SCPTs, N, and that it is modulated with the gate voltage as in the case for a single SCPT. The modulability, however, decreases with the increase in N, which is demonstrated to be mostly because of the charge-state fluctuations of either islands of the constituent SCPTs caused by the capacitive coupling among them. A practically possible method of improving the modulability is also discussed.