Robust Quantum Control via Gaussian-Apodized Phase Modulation (GAPM): A Geometric Approach to Static Dephasing

We propose a geometric control ansatz for mitigating static dephasing errors in superconducting qubit architectures. By combining a Gaussian amplitude envelope with a parameterized adiabatic phase chirp, we construct a "Gaussian-Apodized Phase-Modulated" (GAPM) pulse. We numerically optimize the phase modulation depth using a closed-loop Nelder-Mead algorithm. Our simulations demonstrate that for a 100 ns gate duration subject to substantial static detuning (Δ = 0.5 MHz), the GAPM ansatz achieves a gate fidelity of 99.73% (Infidelity 2.68 × 10⁻³). This represents a significant improvement over standard square pulses, offering a computationally efficient path toward robust quantum logic gates without the overhead of full gradient-based optimization.