Multilevel resonant tunneling in the presence of flux and charge noise

TL;DR

This paper provides a detailed theoretical analysis of macroscopic resonant tunneling in flux qubits, elucidating how flux and charge noise influence tunneling signals and lineshapes, aiding in noise characterization.

Contribution

It introduces a comprehensive derivation of MRT signals considering flux and charge noise effects, including transitions to excited states for better noise source identification.

Findings

Flux noise shapes the ground-to-ground tunneling lineshape.

Charge noise causes broadening of the ground-to-excited tunneling peak.

The model enables distinguishing between flux and charge noise effects.

Abstract

Macroscopic resonant tunneling (MRT) in flux qubits is an important experimental tool for extracting information about noise produced by a qubit's surroundings. Here we present a detailed derivation of the MRT signal in the RF-SQUID flux qubit allowing for effects of flux and charge fluctuations on the interwell and intrawell transitions in the system. Taking into consideration transitions between the ground state in the initial well and excited states in the target well enable us to characterize both flux and charge noise source affecting the operation of the flux qubit. The MRT peak is formed by the dominant noise source affecting specific transition, with flux noise determining the lineshape of the ground to ground tunneling, whereas charge noise reveals itself as additional broadening of the ground to excited peak.