Analytically Solvable Robust Single-Qubit Gates for Multi-Qubit Systems with Unwanted Couplings

Abstract: Couplings between qubits, while essential for generating multi-qubit entanglement, can induce crosstalk errors that significantly degrade single-qubit gate fidelity. In this paper, we present a novel non-perturbative analytical framework for constructing high-fidelity single-qubit gates in the presence of unwanted couplings. By uncovering a geometric structure in SU(2) dynamics, we derive a crosstalk suppression condition: The dynamics must trace a closed loop on the surface of a 2-sphere with net-zero enclosed area, with the pulse waveform corresponding to the geodesic curvature of the loop. This method integrates seamlessly with noise-resilient optimization techniques. Numerical examples demonstrate its efficacy, achieving high-fidelity single-qubit gates in two- and three-qubit systems with strong couplings beyond the perturbative regime while remaining robust to fluctuating noise.