Current-Phase Relation and Josephson Inductance of Superconducting Cooper Pair Transistor

TL;DR

This study measures the Josephson inductance of a superconducting Cooper pair transistor using microwave reflection, revealing a strongly non-sinusoidal current-phase relation near the charge degeneracy point.

Contribution

It provides the first detailed measurement of the current-phase relation and Josephson inductance of a SCPT using microwave reflection techniques.

Findings

Josephson inductance varies with charge and phase.

Current-phase relation is strongly non-sinusoidal near charge degeneracy.

Method demonstrates a new way to probe SCPT properties.

Abstract

We have investigated the Josephson inductance $L_J$ of a Superconducting Cooper Pair Transistor (SCPT). We traced the inductance using microwave reflection measurements on a tuned resonance circuit in which a SCPT was mounted in parallel to a $ \sim 200$ pH strip line inductance. When the inverse of the Josephson inductance, determined on the charge-phase bias plane for a SCPT with a Josephson to Coulomb energy ratio of $E_J/E_C =1.75$, is integrated over the phase, we obtain a current-phase relation, which is strongly non-sinusoidal near the charge degeneracy point.