Optically-pumped magnetometers constitute a valuable tool for imaging biological magnetic signals without cryogenic cooling. Nowadays, numerous developments are being pursued using alkali-based magnetometers, which have demonstrated excellent sensitivities in the spin-exchange relaxation free (SERF) regime that requires heating to >100 °C. In contrast, metastable helium-4 based magnetometers work at any temperature, which allows a direct contact with the scalp, yielding larger signals and a better patient comfort. However former ⁴He magnetometers displayed large noises of >200 fT/Hz^1/2 with 300-Hz bandwidth. We describe here an improved magnetometer reaching a sensitivity better than 50 fT/Hz^1/2, nearly the photon shot noise limit, with a bandwidth of 2 kHz. Like other zero-field atomic magnetometers, these magnetometers can be operated in closed-loop architecture reaching several hundredths nT of dynamic range. A small array of 4 magnetometers operating in a closed loop has been tested with a successful correction of the cross-talks.

中文翻译：

---

用于室温生物医学成像的 Helium-4 磁力计：面向集体操作和光子噪声有限的灵敏度

光泵磁力计是一种无需低温冷却即可对生物磁信号进行成像的宝贵工具。如今，人们正在使用碱基磁力计进行大量开发，这些磁力计在需要加热至 > 100 °C 的自旋交换弛豫 (SERF) 状态下表现出优异的灵敏度。相比之下，基于亚稳态氦 4 的磁力计可在任何温度下工作，它允许与头皮直接接触，产生更大的信号和更好的患者舒适度。然而，以前的⁴ He 磁力计在 300 Hz 带宽下显示 >200 fT/Hz ^{1/2 的}大噪声。我们在此描述了一种改进的磁力计，其灵敏度高于 50 fT/Hz ^1/2，接近光子散粒噪声极限，带宽为 2 kHz。与其他零场原子磁力计一样，这些磁力计可以在动态范围达到百分之几 nT 的闭环架构中运行。在闭环中运行的 4 个磁力计的小阵列已经过测试，串扰校正成功。