Sensitivity threshold defines the optimal spin subset for ensemble quantum sensing

TL;DR

This paper introduces a method to identify the optimal subset of spins in an ensemble for quantum sensing, significantly improving sensitivity by accounting for inhomogeneities and residual aberrations.

Contribution

It derives an analytic sensitivity expression and sensitivity thresholds, enabling the selection of optimal spin subsets in inhomogeneous environments, with practical implementation via digital holography.

Findings

Optimal subsets improve sensitivity up to tenfold.

Residual aberrations cause less than 1 dB sensitivity loss.

Framework extends quantum sensing to heterogeneous environments.

Abstract

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.