Decoherence processes in a current biased dc SQUID

TL;DR

This paper investigates decoherence in a current biased dc SQUID modeled as a two-level quantum system, measuring relaxation and noise sources to understand decoherence mechanisms.

Contribution

It provides experimental measurements of relaxation times and noise sources, explaining decoherence in a dc SQUID through flux and current noise analysis.

Findings

Decoherence times are quantified for the two-level system.

Flux and current noise sources fully account for decoherence.

Measured noise spectra match theoretical predictions.

Abstract

A current bias dc SQUID behaves as an anharmonic quantum oscillator controlled by a bias current and an applied magnetic flux. We consider here its two level limit consisting of the two lower energy states $| 0 \right>$ and $| 1 \right>$. We have measured energy relaxation times and microwave absorption for different bias currents and fluxes in the low microwave power limit. Decoherence times are extracted. The low frequency flux and current noise have been measured independently by analyzing the probability of current switching from the superconducting to the finite voltage state, as a function of applied flux. The high frequency part of the current noise is derived from the electromagnetic environment of the circuit. The decoherence of this quantum circuit can be fully accounted by these current and flux noise sources.