Probing Noise in Flux Qubits via Macroscopic Resonant Tunneling

TL;DR

This paper uses macroscopic resonant tunneling in flux qubits to characterize low-frequency flux noise, revealing a quantum environment as the main noise source, with noise amplitude weakly dependent on temperature below 70 mK.

Contribution

It introduces a method to probe flux noise in flux qubits via resonant tunneling, identifying the quantum environment as the dominant noise source.

Findings

Gaussian noise profile shifted from resonance point

Weak temperature dependence of noise amplitude below 70 mK

Quantum environment causes dominant low-frequency flux noise

Abstract

Macroscopic resonant tunneling between the two lowest lying states of a bistable RF-SQUID is used to characterize noise in a flux qubit. Measurements of the incoherent decay rate as a function of flux bias revealed a Gaussian shaped profile that is not peaked at the resonance point, but is shifted to a bias at which the initial well is higher than the target well. The r.m.s. amplitude of the noise, which is proportional to the decoherence rate 1/T_2^*, was observed to be weakly dependent on temperature below 70 mK. Analysis of these results indicates that the dominant source of low frequency (1/f) flux noise in this device is a quantum mechanical environment in thermal equilibrium.