A Compact Broadband Purcell Filter for Superconducting Quantum Circuits in a 3D Flip-Chip Architecture

Abstract:Fast and high-fidelity qubit readout requires strong coupling between the readout resonator and the feedline. However, such coupling unavoidably enhances qubit decay through the Purcell effect. We present a four-pole broadband Purcell filter implemented on a 3D flip-chip platform to overcome this trade-off. The filter provides a flat 1 GHz passband centered at 7.68 GHz and achieves more than 45 dB suppression at typical qubit frequencies. We demonstrate the filter's compatibility with multiplexed readout using a test chip that integrates six floating readout resonators strongly coupled within the passband. The chip is fabricated using a 150 nm Niobium (Nb) thin-film process and characterized at 20 mK in a cryogenic measurement setup. We also develop an analytical model that accurately captures the filter response and determines the resonance frequencies and external quality factors of the floating resonators directly from their physical geometry, enabling rapid circuit synthesis and design optimization. The proposed design is compact and fabrication-tolerant, making it a practical solution for large-scale superconducting quantum processors.

13 pages, 14 figures. Thanks to this http URL. Sean McClure. A typo in Eq.(15) is corrected in this version

arXiv:2603.16693 [quant-ph]

(or arXiv:2603.16693v3 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2603.16693 Focus to learn more arXiv-issued DOI via DataCite

IEEE Trans. Microw. Theory Tech., vol. 74, no. 8, pp. 7463-7475, Aug. 2026

https://doi.org/10.1109/TMTT.2026.3705158 Focus to learn more DOI(s) linking to related resources

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