Relaxation of Josephson qubits due to strong coupling to two-level systems

TL;DR

This paper studies how Josephson qubits lose energy due to interactions with many two-level systems, revealing that dense collections of weakly coupled fluctuators can cause effects previously attributed to strongly coupled individual fluctuators.

Contribution

It demonstrates that avoided level crossings in qubits can result from many weakly coupled fluctuators, not just strongly coupled single fluctuators, expanding understanding of qubit decoherence.

Findings

Avoided level crossings can be caused by dense fluctuator spectra.

Weakly coupled fluctuators can mimic effects of strong coupling.

Implications for improving qubit coherence by understanding environmental interactions.

Abstract

We investigate the energy relaxation (T1) process of a qubit coupled to a bath of dissipative two-level fluctuators (TLF). We consider the fluctuators strongly coupled to the qubit both in the limit of spectrally separated single TLF's as well as in the limit of spectrally dense TLF's. We conclude that the avoided level crossings, usually attributed to very strongly coupled single TLF's, could also be caused by many weakly coupled spectrally dense fluctuators.