Quadrature-symmetric pulse scheme for robust quantum control beyond the ideal-pulse approximation
Phys. Rev. Applied 26, 034032 – Published 15 September, 2026
DOI: https://doi.org/10.1103/b4tk-xgl9
Abstract
PulsePol is an elegantly designed pulse-sequence-based quantum control scheme that enables polarization transfer between electron and nuclear spins. However, previous analyses of PulsePol assumed very strong, close to ideal, instantaneous microwave pulses, which is rarely achievable as one goes to higher magnetic fields. We revisit the PulsePol scheme under finite-pulse constraints and show that its performance significantly degrades because of finite-pulse effects. Using bimodal Floquet theory, we identify the symmetry-breaking mechanism responsible for this deteriorating fidelity. By phase adjustment, we reestablish the proper symmetry of the interaction-frame spin Hamiltonian—leading to a sequence called Q-PulsePol, where ‘Q’ reflects the restored quadrature symmetry. Our results demonstrate robustness to finite-pulse effects and improved polarization transfer efficiency, establishing Q-PulsePol as a practical and reliable scheme for bulk hyperpolarization of nuclear spins in solid-state using a single-mode (zero-quantum or double-quantum) transfer. This work bridges idealized quantum control with realistic pulse engineering, establishing design rules for spin-based quantum-control protocols.
