Effect of Measurement on the Periodicity of the Coulomb Staircase of a Superconducting Box

TL;DR

This paper investigates how a Single Cooper Pair Transistor electrometer affects charge measurements on a superconducting box, revealing quasiparticle poisoning impacts and proposing a new switching current method to restore accurate 2e periodicity.

Contribution

It demonstrates the back-action effects of the electrometer on charge measurements and introduces a novel switching current technique to eliminate this influence.

Findings

Back-action causes e-periodic charge signals due to quasiparticle poisoning.

Quasiparticle poisoning rate is proportional to tunneling events in the electrometer.

New measurement method restores 2e charge periodicity by switching current modulation.

Abstract

We report on the effect of the back-action of a Single Cooper Pair Transistor electrometer (E) on the measurement of charge on the island of a superconducting box (B). The charge is e-periodic in the gate bias of B when E is operated near voltages 2Delta/e or 4Delta/e. We show that this is due to quasiparticle poisoning of B at a rate proportional to the number of quasiparticle tunneling events in E per second. We are able to eliminate this back action and recover 2e charge periodicity using a new measurement method based on switching current modulation of E.