Scalable superconducting quantum processors require balancing critical constraints in coherence, control complexity, and spectral crowding. Fixed-frequency architectures suppress flux noise and simplify control via all-microwave operations but remain limited by residual ZZ crosstalk. Here we propose a microwave-activated three-qubit gate protocol for fixed-frequency transmon qubits in the large-detuning regime (∣Δ∣≫g), leveraging the third-order nonlinear interaction to coherently exchange ∣001⟩↔∣110⟩ states. By incorporating a phase-compensated optimization protocol, numerical simulations demonstrate a high average gate fidelity exceeding 99.9%. Systematic error analysis identifies static long-range ZZ coupling as the dominant error source in multi-qubit systems, which can be suppressed via operations in the large-detuning regime (∼1 GHz). The protocol maintains process fidelities exceeding 98% under decoherence, while demonstrating intrinsic robustness to fabrication-induced parameter variations and compatibility with existing all-microwave two-qubit gate architectures. This hardware-efficient strategy advances scalable quantum computing systems by improving coherence properties, reducing spectral congestion, and expanding the experimental toolkit for error-resilient quantum operations in the noisy intermediate-scale quantum era.
@article{arxiv.2504.21346,
title = {Microwave-activated high-fidelity three-qubit gate scheme for fixed-frequency superconducting qubits},
author = {Kui Zhao and Wei-Guo Ma and Ziting Wang and Hao Li and Kaixuan Huang and Yun-Hao Shi and Kai Xu and Heng Fan},
journal= {arXiv preprint arXiv:2504.21346},
year = {2025}
}