We introduce a multimode superconducting inductor architecture that enables radio-frequency reflectometry at multiple discrete frequencies up to 2 GHz, addressing limitations of conventional single-mode designs. The spiral inductor's distributed inter-turn capacitance yields distinct resonant modes with varied impedance-matching conditions. By probing a quantum dot across several modes, we extract tunneling rates over a broad frequency range and identify signatures of nearby charge defects. Using one of the higher-order modes, we demonstrate single-shot spin readout via a radio-frequency single-electron transistor (RF-SET), achieving singlet-triplet readout with an integration time of 8 us and a readout fidelity of 98%. These results establish multimode inductance as a scalable and flexible component for fast spin-qubit readout and device-quality characterization.
@article{arxiv.2512.05087,
title = {Multimode RF Reflectometry for Spin Qubit Readout and Device Characterization},
author = {Joffrey Rivard and Alexis Morel and Olivier Romain and El Bachir Ndiaye and Idris Aboubakari and Christian Lupien and Clément Godfrin and Julien Jussot and Stefan Kubicek and Kristiaan De Greve and Danny Wan and Claude Rohrbacher and Eva Dupont-Ferrier},
journal= {arXiv preprint arXiv:2512.05087},
year = {2025}
}