Characterisation of spatial charge sensitivity in a multi-mode superconducting qubit

TL;DR

This paper investigates the charge sensitivity of a multi-mode superconducting qubit, revealing complex charge-fluctuation behaviors and demonstrating its potential as a spatial charge detector, which advances understanding of decoherence mechanisms.

Contribution

It provides the first detailed characterization and theoretical modeling of charge sensitivity in multi-mode superconducting qubits, highlighting their utility for charge detection.

Findings

Observed sensitivity to four charge-parity configurations

Tracked two independent charge-offset drifts over hours

Developed a predictive theory matching experimental results

Abstract

Understanding and suppressing sources of decoherence is a leading challenge in building practical quantum computers. In superconducting qubits, low frequency charge noise is a well-known decoherence mechanism that is effectively suppressed in the transmon qubit. Devices with multiple charge-sensitive modes can exhibit more complex behaviours, which can be exploited to study charge fluctuations in superconducting qubits. Here we characterise charge-sensitivity in a superconducting qubit with two transmon-like modes, each of which is sensitive to multiple charge-parity configurations and charge-offset biases. Using Ramsey interferometry, we observe sensitivity to four charge-parity configurations and track two independent charge-offset drifts over hour timescales. We provide a predictive theory for charge sensitivity in such multi-mode qubits which agrees with our results. Finally, we demonstrate the utility of a multi-mode qubit as a charge detector by spatially tracking local-charge drift.