Femtotesla direct magnetic gradiometer using a single multipass cell

TL;DR

This paper presents a highly sensitive magnetic gradiometer using a single multipass cell with optical pumping in rubidium atoms, achieving femtotesla-level sensitivity and reduced atomic diffusion effects.

Contribution

The work introduces a novel single-cell multipass design for a direct magnetic gradiometer with enhanced sensitivity and noise reduction capabilities.

Findings

Achieved a gradiometer sensitivity of 10.1 fT/cm√Hz.

Demonstrated reduced atomic diffusion effects due to multipass design.

Validated theoretical predictions with experimental results.

Abstract

We describe a direct gradiometer using optical pumping with opposite circular polarization in two $^{87}$Rb atomic ensembles within a single multipass cell. A far-detuned probe laser undergoes a near-zero paramagnetic Faraday rotation due to the intrinsic subtraction of two contributions exceeding 3.5 rad from the highly-polarized ensembles. We develop analysis methods for the direct gradiometer signal and measure a gradiometer sensitivity of $10.1$ fT/cm$\sqrt{\mathrm{Hz}}$. We also demonstrate that our multipass design, in addition to increasing the optical depth, provides a fundamental advantage due to the significantly reduced effect of atomic diffusion on the spin noise time-correlation, in excellent agreement with theoretical estimate.