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 multiqubit systems, which can be suppressed via operations in the large-detuning regime (approximately 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.

Paper link: https://journals.aps.org/prapplied/abstract/10.1103/l721-33qk