We describe a direct gradiometer using optical pumping with opposite circular polarization in two ${}^{87}\mathrm{Rb}$ 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 $\mathrm{fT}/\mathrm{cm}\sqrt{\mathrm{Hz}}$. 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 the theoretical estimate.

中文翻译：

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使用单个多通道电池的Femtotesla直接电磁梯度仪

我们描述了一种直接梯度仪，它在两个方向上使用具有相反圆偏振的光泵浦 ${}^{87}b$单个多通道单元内的原子团。由于从高偏振合奏中固有地减去了两个超过3.5 rad的贡献，因此远失谐的探针激光器经历了接近零的顺磁法拉第旋转。我们开发了直接梯度仪信号的分析方法，并将梯度仪的灵敏度测量为10.1$T/\mathrm{厘米}\sqrt{\mathrm{赫兹}}$。我们还证明，除了增加光学深度之外，我们的多程设计还提供了基本优势，这是由于原子扩散对自旋噪声时间相关性的影响显着降低，与理论估计非常吻合。