Flexible Readout and Unconditional Reset for Superconducting Multi-Qubit Processors with Tunable Purcell Filters

TL;DR

This paper presents a scalable superconducting qubit architecture with tunable Purcell filters that enable high-fidelity readout, fast unconditional reset, and coherence preservation, advancing quantum error correction capabilities.

Contribution

The authors introduce a frequency-tunable nonlinear Purcell filter architecture that enhances readout fidelity, enables rapid unconditional reset, and mitigates decoherence in multi-qubit superconducting processors.

Findings

Achieved 99.3% readout fidelity without quantum-limited amplifiers.

Realized unconditional reset of leakage and qubit states within 200 ns with errors ≤1%.

Demonstrated suppression of photon-induced dephasing and the Purcell effect.

Abstract

Achieving high-fidelity qubit readout and reset while preserving qubit coherence is essential for quantum error correction and other advanced quantum algorithms. Here, we design and experimentally demonstrate a scalable architecture employing frequency-tunable nonlinear Purcell filters, enabling flexible readout and fast unconditional reset of multiple superconducting qubits. Our readout protocol dynamically adjusts the effective linewidth of the readout resonator through a tunable Purcell filter, optimizing the signal-to-noise ratio during measurement while suppressing photon noise during idle periods. We achieve a readout fidelity of $99.3\%$ without any quantum-limited amplifier, even with a small dispersive shift. Moreover, by leveraging a reset channel formed via the adjacent coupling between the filter and the coupler, we realize unconditional qubit reset of both leakage-induced $|2\rangle$ and $|1\rangle$ states within 200 ns and reset of the $|1\rangle$ state alone within 75 ns, with error rates $\leq 1\%$. The filter also mitigates both photon-induced dephasing and the Purcell effect, thereby preserving qubit coherence. This scalable Purcell filter architecture shows exceptional performance in qubit readout, reset, and protection, marking it as a promising hardware component for advancing fault-tolerant quantum computing systems.