Nondemolition readout and high-fidelity unconditional reset of qubits are key requirements for practical quantum computation. For superconducting qubits, readout and reset are typically realized using resonators based on dispersive approximation. However, violations of the approximation often lead to detrimental effects on the qubit. In this work, we demonstrate nondemolition fluorescence readout and high-fidelity unconditional reset of a fluxonium qubit via dissipation engineering without employing a resonator. We design and implement a planar filter to protect the qubit from energy relaxation while enhancing the relaxation of the readout transition. By appropriately selecting the readout transition, we achieve fluorescence readout with enhanced quantum nondemolitionness. We also realize fast, high-fidelity, and all-microwave unconditional reset of the fluxonium qubit. These results highlight the potential of superconducting quantum computing architectures without relying on dispersive interaction between qubits and resonators.

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• Superconducting qubits