Rapid reset and readout of qubit states are essential for quantum error correction, yet accelerating these operations through stronger coupling to a dissipative environment inevitably increases qubit decay via the Purcell effect. Here we present a broadband Purcell filter that decouples the reset and readout paths, enabling both operations to be independently optimized without compromising qubit coherence. The filter employs two engineered notches - an intrinsic notch and a bandstop notch - to provide broadband Purcell protection, together with an additional reset stub that creates a reset mode below the protected band. To enable fast reset while suppressing filter-mediated interactions between qubits, we couple each qubit to a dedicated reset resonator. We experimentally demonstrate Purcell-limited relaxation times exceeding 1 ms across a 1.2 GHz bandwidth, simultaneously with 500 ns readout without a Josephson parametric amplifier and 100 ns reset with 99.6% efficiency. The reset resonator is designed with a deliberate kappa-chi mismatch, which suppresses photon-shot-noise-induced dephasing by a factor of 70 compared to the readout resonator. Our work provides a scalable hardware solution that resolves the traditional trade-off between fast qubit operations and qubit protection, advancing the prospects for fault-tolerant quantum computing.Rapid reset and readout of qubit states are essential for quantum error correction, yet accelerating these operations through stronger coupling to a dissipative environment inevitably increases qubit decay via the Purcell effect. Here we present a broadband Purcell filter that decouples the reset and readout paths, enabling both operations to be independently optimized without compromising qubit coherence. The filter employs two engineered notches - an intrinsic notch and a bandstop notch - to provide broadband Purcell protection, together with an additional reset stub that creates a reset mode below the protected band. To enable fast reset while suppressing filter-mediated interactions between qubits, we couple each qubit to a dedicated reset resonator. We experimentally demonstrate Purcell-limited relaxation times exceeding 1 ms across a 1.2 GHz bandwidth, simultaneously with 500 ns readout without a Josephson parametric amplifier and 100 ns reset with 99.6% efficiency. The reset resonator is designed with a deliberate kappa-chi mismatch, which suppresses photon-shot-noise-induced dephasing by a factor of 70 compared to the readout resonator. Our work provides a scalable hardware solution that resolves the traditional trade-off between fast qubit operations and qubit protection, advancing the prospects for fault-tolerant quantum computing.

quant-pharXiv:2609.14081Sep 15, 20260 citations

Quantum analysis of a bandpass Purcell filter for accurate qubit readout

Eyob Alebachew Sete, John M. Martinis, Alexander N. Korotkov

Bulletin of the American Physical SocietyMar 5, 20150 citations

Fast dispersive, Purcell-filtered measurement and reset using smooth and simple analytic pulse shapes

Lukas F. Buchmann, Felix Motzoi, Christian Dickel

Bulletin of the American Physical SocietyMar 5, 20190 citations

Purcell-Engineered Hybrid Coupler for Leakage-Suppressed Robust CZ Gates

Hui Wang, Feng Bao, Yan-Jun Zhao +1 more

We propose a Purcell-engineered notch-filter hybrid coupler for superconducting controlled- $Z$ (CZ) gates that combines coherent interaction engineering with leakage-selective dissipation. The architecture integrates a nonlinear transmon coupler with a coupled Purcell-filter and notch-resonator subsystem, providing additional control over both the coherent interaction pathways and the engineered dissipative environment. The filter branch reshapes the effective interaction pathways, while the notch resonator further tailors the frequency response of the coupled filter network and preserves strong leakage-selective dissipation. Using dressed-eigenstate analysis together with Lindblad master-equation simulations, we show that the proposed architecture substantially reduces leakage and retains high-fidelity, low-leakage operation compared with an optimized single-transmon coupler while remaining robust over a broad range of coherence assumptions and device parameters. The gate analysis reconstructs the projected computational quantum channel and therefore retains the phase information required to distinguish a CZ operation from identity. The nominal operating point occurs at $t_{\rm CZ}=327.46~\mathrm{ns}$ with $F_{\rm avg}^{\rm CZ}=99.714\%$ , $L_{\rm avg}=8.78\times10^{-4}$ , and $L_{\rm max}=2.04\times10^{-3}$ . A minimax timing-robust operating point at $327.20~\mathrm{ns}$ maintains $F_{\rm avg}^{\rm CZ}\geq99.590\%$ over a $\pm0.50~\mathrm{ns}$ timing window. These results demonstrate that engineered dissipation complements conventional coherent interaction engineering and provides an additional design degree of freedom for realizing robust, high-fidelity superconducting CZ gates.We propose a Purcell-engineered notch-filter hybrid coupler for superconducting controlled-$Z$ (CZ) gates that combines coherent interaction engineering with leakage-selective dissipation. The architecture integrates a nonlinear transmon coupler with a coupled Purcell-filter and notch-resonator subsystem, providing additional control over both the coherent interaction pathways and the engineered dissipative environment. The filter branch reshapes the effective interaction pathways, while the notch resonator further tailors the frequency response of the coupled filter network and preserves strong leakage-selective dissipation. Using dressed-eigenstate analysis together with Lindblad master-equation simulations, we show that the proposed architecture substantially reduces leakage and retains high-fidelity, low-leakage operation compared with an optimized single-transmon coupler while remaining robust over a broad range of coherence assumptions and device parameters. The gate analysis reconstructs the projected computational quantum channel and therefore retains the phase information required to distinguish a CZ operation from identity. The nominal operating point occurs at $t_{\rm CZ}=327.46~\mathrm{ns}$ with $F_{\rm avg}^{\rm CZ}=99.714\%$, $L_{\rm avg}=8.78\times10^{-4}$, and $L_{\rm max}=2.04\times10^{-3}$. A minimax timing-robust operating point at $327.20~\mathrm{ns}$ maintains $F_{\rm avg}^{\rm CZ}\geq99.590\%$ over a $\pm0.50~\mathrm{ns}$ timing window. These results demonstrate that engineered dissipation complements conventional coherent interaction engineering and provides an additional design degree of freedom for realizing robust, high-fidelity superconducting CZ gates.

quant-pharXiv:2607.23463Jul 28, 20260 citations

We propose a Purcell-engineered notch-filter hybrid coupler for superconducting controlled-

Z

(CZ) gates that combines coherent interaction engineering with leakage-selective dissipation. The architecture integrates a nonlinear transmon coupler with a coupled Purcell-filter and notch-resonator subsystem, providing additional control over both the coherent interaction pathways and the engineered dissipative environment. The filter branch reshapes the effective interaction pathways, while the notch resonator further tailors the frequency response of the coupled filter network and preserves strong leakage-selective dissipation. Using dressed-eigenstate analysis together with Lindblad master-equation simulations, we show that the proposed architecture substantially reduces leakage and retains high-fidelity, low-leakage operation compared with an optimized single-transmon coupler while remaining robust over a broad range of coherence assumptions and device parameters. The gate analysis reconstructs the projected computational quantum channel and therefore retains the phase information required to distinguish a CZ operation from identity. The nominal operating point occurs at

t_{\rm CZ}=327.46~\mathrm{ns}

with

F_{\rm avg}^{\rm CZ}=99.714\%

L_{\rm avg}=8.78\times10^{-4}

, and

L_{\rm max}=2.04\times10^{-3}

. A minimax timing-robust operating point at

327.20~\mathrm{ns}

maintains

F_{\rm avg}^{\rm CZ}\geq99.590\%

over a

\pm0.50~\mathrm{ns}

timing window. These results demonstrate that engineered dissipation complements conventional coherent interaction engineering and provides an additional design degree of freedom for realizing robust, high-fidelity superconducting CZ gates.