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arXiv:2108.11358 · PRX Quantum

Fast Multiqubit Gates through Simultaneous Two-Qubit Gates

Xiu Quan Gu, Jorge Fernández-Pendás, Pontus Vikstål, Tahereh Abad, Christopher Warren, Andreas Bengtsson, Giovanna Tancredi, Vitaly S. Shumeiko, Jonas Bylander, Göran Johansson, Anton Frisk Kockum

Published Dec 8, 2021• 49 citations
arXivHTMLPDF

Abstract

A recipe to create multi-qubit gates that uses existing quantum hardware-- without any additional components, complicated pulse shapes, or changes in design--is proposed, promising a reduction in circuit depth, and executions that are faster than their two-qubit counterparts.
DOI
10.1103/prxquantum.2.040348

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Practical quantum advantage hinges on executing deep quantum circuits within the coherence limits of noisy intermediate-scale quantum processors. The absence of native, high-fidelity multi-qubit gates remains a major bottleneck, as their decomposition into single- and two-qubit gates leads to prohibitive depth and error overhead. Here, we propose a hardware-efficient protocol that directly implements a native controlled-controlled-Z (CCZ) gate in a tunable-coupler superconducting circuit. Our theoretical protocol activates a resonant three-qubit interaction via a time-frequency correlated virtual process, explicitly relying on the dynamic resonant exchange within the ∣101⟩↔∣020⟩|101\rangle \leftrightarrow |020\rangle∣101⟩↔∣020⟩ transition manifold. This approach is compatible with standard tunable-coupler architectures without requiring additional control resources. Through a systematic calibration workflow combining pulse shaping and active cancellation of residual phases, we demonstrate a gate fidelity exceeding 99\% within 165 ns165\,\mathrm{ns}165ns -- significantly outperforming decomposed sequences. Comprehensive error budgeting confirms that the gate performance remains robust against realistic experimental imperfections. Furthermore, we show that this scheme can be naturally extended to a continuous CCPhase(θ)\mathrm{CCPhase}(θ)CCPhase(θ) gate set. This work provides a direct, high-fidelity route to three-qubit entanglement, offering promising prospects for efficient execution of quantum algorithms on near-term superconducting hardware.