Dephasing of Josephson qubits close to optimal points

TL;DR

This paper investigates how tuning Josephson qubits to optimal points reduces decoherence, analyzing dephasing caused by 1/f noise and the transition from quadratic to linear coupling regimes.

Contribution

It provides a detailed analysis of dephasing mechanisms near optimal points, including the effects of various noise sources and the crossover to linear coupling.

Findings

Quadratic coupling at optimal points significantly suppresses dephasing.

Dephasing behavior differs between free induction decay and spin-echo experiments.

Multiple noise sources influence the dephasing dynamics.

Abstract

Decoherence of Josephson qubits can be substantially reduced by tuning their parameters to optimal operation points, with only quadratic coupling to fluctuations. We analyze dephasing due to 1/f noise for a two-level system, detuned from an optimal point, i.e., the crossover to the linear-coupling regime, both for free induction decay and for spin-echo experiments. Influence of several noise sources is also discussed.