Impact of qubit anharmonicity on near-resonant Rabi oscillations

TL;DR

This paper explores how qubit anharmonicity influences near-resonant Rabi oscillations and gate errors, providing experimental validation of analytical models and insights for improving quantum gate fidelity.

Contribution

It presents a detailed experimental and analytical study of anharmonicity effects on Rabi oscillations and gate errors in fluxonium qubits under typical two-qubit gate conditions.

Findings

Rabi frequency squared depends linearly on drive amplitude squared

Experimental data aligns with analytical predictions

Leakage and phase errors are analyzed for CZ gate implementation

Abstract

Precise quantum control relies on a deep understanding of the dynamics of quantum systems under external drives. This study investigates the impact of anharmonicity on qubit dynamics under conditions typical for two-qubit entangling gates activated by weak near-resonant microwave drives. We measure the Rabi oscillation frequency as a function of drive amplitude and detuning. Our results reveal a linear dependence of the squared Rabi frequency on the squared drive amplitude, which relates to the ratio of detuning to anharmonicity, demonstrating strong agreement between experimental data and analytical predictions. Additionally, we analyze the leakage and phase errors arising from inaccurate Rabi frequency adjustments in the CZ gate implementation on fluxonium qubits driven by a microwave signal applied to the coupler.