Sub-Ensemble Isolation in SERF Magnetometry Enabled by Micrometer-Scale Polarization Control

TL;DR

This paper introduces a novel method for creating independent sub-ensembles within a single SERF magnetometer by manipulating polarization at the micrometer scale, enabling high spatial resolution in magnetic sensing.

Contribution

The study develops a miniaturized vapor cell and polarization metasurface to achieve position-dependent atomic anisotropy, allowing sub-ensemble isolation in SERF magnetometry.

Findings

Achieved 0.22 V/nT average scale factor per channel.

Measured crosstalk ratio up to 32 dB between sub-ensembles.

Demonstrated enhanced spatial resolution for neural biomagnetism mapping.

Abstract

Conventional understanding of spin-exchange relaxation-free (SERF) atom ensemble pertains to the common perception that the rapid exchange of atom state finally results in uniform time evolution of the whole ensemble. However, in this study, we demonstrate that by manipulation of pumping polarization in micro-meter level, misalignment between the time evolution of different sub-ensemble can be created within single SERF ensemble with unprecedent independency. A novel pumping system consists of a miniaturized $^{87}$Rb vapor cell and a space-variant polarization metasurface is developed for the prove of concept. Our method induces position-dependent atomic anisotropy in both pumping and absorption into the thermal atomic ensemble. By constructing calculated Zeeman-sublevel populations in SERF regime, distinct sensing channels are generated with 0.22 $V\ nT^{-1}$ average scale factor, which is comparable with single channel generated by single SERF ensemble. Average crosstalk ratio between adjacent channels (between micron scale sub-ensembles) are measured up to 32 dB, through the excitation of fictitious magnetic field (3.5 nT, 30 Hz), which is measured as 20 dB without sub-ensemble isolation in same experimental condition. Our work demonstrates unprecedented spatial resolution in SERF magnetometry which hold new promises for applications including high-spatial resolution neural biomagnetism mapping and portable magnetism measurement device.