Crosstalk in Multi-Qubit Fluxonium Architectures with Transmon Couplers

TL;DR

This paper analyzes the scalability of fluxonium qubit architectures with transmon couplers, identifying crosstalk issues and proposing methods to reduce errors for high-fidelity quantum operations.

Contribution

It provides a numerical study of crosstalk effects in fluxonium architectures with transmon couplers and suggests strategies to mitigate errors for scalable quantum computing.

Findings

Spectator qubit crosstalk limits fidelity below 90% in naive scaling.

Reducing coupling strength and off-position tuning suppresses errors below 10^{-4}.

Operation resilience to capacitive and microwave crosstalk is demonstrated.

Abstract

In recent years, several architectures have been proposed for implementing two-qubit operations on fluxonium superconducting qubits. A particularly promising approach, which was demonstrated experimentally by Refs. [1,2], employs a transmon superconducting qubit as a tunable coupler between the fluxonium qubits. These experiments have shown that the transmon coupler enables fast, high-fidelity two-qubit operations while suppressing unwanted ZZ crosstalk between the fluxonium qubits. In this work, we numerically study the scalability of this architecture. We find that, when trivially scaling this architecture, crosstalk from spectator qubits limits the gate fidelity to below 90%. We show that these spectator errors can be reduced to below $10^{-4}$ by reducing the coupling strength and by dynamically tuning transmons that are not used for a two-qubit operation to an off position. We further investigate the resilience of the operation to direct capacitive coupling between the transmon couplers and to microwave crosstalk.