Dynamics of parametric fluctuations induced by quasiparticle tunneling in superconducting flux qubits

TL;DR

This paper investigates how quasiparticle tunneling causes parametric fluctuations in superconducting flux qubits, revealing their impact on decoherence through spectroscopic measurements and temperature-dependent transition rates.

Contribution

It provides experimental evidence linking quasiparticle tunneling to parametric fluctuations and decoherence in flux qubits, highlighting the significance of quasiparticles as a noise source.

Findings

Fluctuator manifests as a doublet line in spectroscopy.

Transition rate increases with temperature from 40 to 158 mK.

Quasiparticle tunneling induces the observed fluctuations.

Abstract

We present experiments on the dynamics of a two-state parametric fluctuator in a superconducting flux qubit. In spectroscopic measurements, the fluctuator manifests itself as a doublet line. When the qubit is excited in resonance with one of the two doublet lines, the correlation of readout results exhibits an exponential time decay which provides a measure of the fluctuator transition rate. The rate increases with temperature in the interval 40 to 158 mK. Based on the magnitude of the transition rate and the doublet line splitting we conclude that the fluctuation is induced by quasiparticle tunneling. These results demonstrate the importance of considering quasiparticles as a source of decoherence in flux qubits.