Kinetics of non-equilibrium quasiparticle tunneling in superconducting charge qubits

TL;DR

This study observes and analyzes non-equilibrium quasiparticle tunneling in superconducting charge qubits at low temperatures, revealing complex tunneling dynamics and temperature-dependent dwell times.

Contribution

It provides the first direct measurement and kinetic theory interpretation of non-equilibrium quasiparticle tunneling in superconducting charge qubits.

Findings

Odd-state dwell times are shorter and non-Poissonian.

Odd-to-even tunneling rates increase at low temperatures.

Quasiparticles tunnel out before thermal equilibrium is reached.

Abstract

We directly observe low-temperature non-equilibrium quasiparticle tunneling in a pair of charge qubits based on the single Cooper-pair box. We measure even- and odd-state dwell time distributions as a function of temperature, and interpret these results using a kinetic theory. While the even-state lifetime is exponentially distributed, the odd-state distribution is more heavily weighted to short times, implying that odd-to-even tunnel events are not described by a homogenous Poisson process. The mean odd-state dwell time increases sharply at low temperature, which is consistent with quasiparticles tunneling out of the island before reaching thermal equilibrium.