Coulomb blockade of Cooper pair tunneling and parity effects in the Cooper pair transistor

TL;DR

This paper investigates how high-impedance electromagnetic environments influence the transport properties of a Cooper Pair Transistor, revealing Coulomb blockade effects and a transition from e- to 2e-periodic modulation.

Contribution

It demonstrates the impact of tunable high-impedance environments on CPT behavior, including Coulomb blockade and parity effects, supported by experimental measurements and quasicharge theory.

Findings

Coulomb blockade of Cooper pair tunneling observed at high impedance

Transition from e-periodic to 2e-periodic modulation with increased impedance

Qualitative agreement between experimental IVCs and quasicharge theory

Abstract

We have measured the Cooper Pair Transistor (CPT) in a tunable electromagnetic environment consisting of four one-dimensional SQUID arrays. The transport properties of the CPT in the high impedance limit, Z_env>>R_Q=6.45~k\Omega, are studied for different ratios of the Josephson coupling energy to the charging energy. As the impedance of the environment is increased, the current-voltage characteristic (IVC) of the CPT develops a Coulomb blockade of Cooper pair tunneling and the measured IVCs agree qualitatively with a theory based on quasicharge dynamics for a CPT. Increasing the impedance of the environment induces a transition in the modulation of the IVC with the gate charge from e-periodic to 2e-periodic.