Enhancement of Josephson quasiparticle current in coupled superconducting single-electron transistors

TL;DR

This paper investigates how the Josephson quasiparticle cycle in superconducting single-electron transistors is affected by strong capacitive coupling, revealing that current in one device can enhance the cycle in the other.

Contribution

It demonstrates experimentally and theoretically that capacitive coupling between two superconducting single-electron transistors enhances the Josephson quasiparticle current in one when the other has a quasiparticle current.

Findings

JQP current is enhanced by the other SSET's quasiparticle current

Strong capacitive coupling influences the JQP cycle

A simplified model reproduces the enhancement effect

Abstract

The Josephson quasiparticle (JQP) cycle in a voltage-biased superconducting single-electron transistor (SSET) combines coherent Cooper pair tunneling with incoherent quasiparticle decay. We have measured the influence of current flow through an independently-biased SSET on the JQP cycle when the two SSET's have a strong mutual capacitive coupling. We find, among other effects, that the JQP current in one SSET is enhanced by the presence of a quasiparticle current in the other SSET. A simplified model of the coupled-SSET system is presented which reproduces the enhancement effect.