Decoherence of flux qubits due to 1/f flux noise

TL;DR

This paper investigates how 1/f flux noise causes decoherence in Josephson-junction flux qubits, identifying noise contributions and demonstrating that at optimal bias, energy relaxation limits coherence.

Contribution

It provides a detailed analysis of flux noise effects on qubit decoherence and quantifies the spectral density of 1/f flux noise at 1 Hz.

Findings

Dephasing due to 1/f flux noise follows a Gaussian decay.

Spectral density of flux noise is about (10^{-6} Φ_0)^2/Hz at 1 Hz.

At optimal bias, energy relaxation limits qubit coherence.

Abstract

We have investigated decoherence in Josephson-junction flux qubits. Based on the measurements of decoherence at various bias conditions, we discriminate contributions of different noise sources. In particular, we present a Gaussian decay function of the echo signal as evidence of dephasing due to $1/f$ flux noise whose spectral density is evaluated to be about $(10^{-6} \Phi_0)^2$/Hz at 1 Hz. We also demonstrate that at an optimal bias condition where the noise sources are well decoupled the coherence observed in the echo measurement is mainly limited by energy relaxation of the qubit.