Lifetime and Coherence of Two-Level Defects in a Josephson Junction

TL;DR

This study measures the lifetime and coherence of two-level defect states in Josephson junctions, revealing power law decay dependence and an optimal coherence at intermediate coupling, explained by the standard TLS model.

Contribution

It provides experimental measurements of TLS lifetimes and coherence in Josephson junctions and analyzes their dependence on interaction strength, advancing understanding of decoherence mechanisms.

Findings

Decay times follow a power law with interaction strength.

Coherence times peak at intermediate coupling strengths.

Results align with the standard TLS model including phonon radiation.

Abstract

We measure the lifetime ($T_{1}$) and coherence ($T_{2}$) of two-level defect states (TLSs) in the insulating barrier of a Josephson phase qubit and compare to the interaction strength between the two systems. We find for the average decay times a power law dependence on the corresponding interaction strengths, whereas for the average coherence times we find an optimum at intermediate coupling strengths. We explain both the lifetime and the coherence results using the standard TLS model, including dipole radiation by phonons and anti-correlated dependence of the energy parameters on environmental fluctuations.