Finite drive power leaves unavoidable spatial gradients in control fields, preventing spin ensembles from reaching the standard-quantum-limit sensitivity. We derive an analytic expression of ensemble sensitivity for inhomogeneous spin sensors and introduce sensitivity thresholds that reveal the optimal spin subset. Applied to both pulsed and continuous-wave magnetometry, the optimal subsets deliver up to a tenfold improvement over conventional schemes relying on nominally uniform regions of the ensembles. We demonstrate phase-only digital holography to implement the optimal subsets and show that residual aberrations add less than 1 dB of sensitivity loss. Our framework imposes no fundamental trade-offs and extends quantum sensing to heterogeneous sensing environments.
@article{arxiv.2512.10549,
title = {Sensitivity threshold defines the optimal spin subset for ensemble quantum sensing},
author = {Suwan I. Kang and Minhyeok Kim and Sanghyo Park and Heonsik Lee and Keunyoung Lee and Donggyu Kim},
journal= {arXiv preprint arXiv:2512.10549},
year = {2025}
}