Kominis I K, Kornack T W, Allred J C, Romalis M V
Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
Nature. 2003 Apr 10;422(6932):596-9. doi: 10.1038/nature01484.
The magnetic field is one of the most fundamental and ubiquitous physical observables, carrying information about all electromagnetic phenomena. For the past 30 years, superconducting quantum interference devices (SQUIDs) operating at 4 K have been unchallenged as ultrahigh-sensitivity magnetic field detectors, with a sensitivity reaching down to 1 fT Hz(-1/2) (1 fT = 10(-15) T). They have enabled, for example, mapping of the magnetic fields produced by the brain, and localization of the underlying electrical activity (magnetoencephalography). Atomic magnetometers, based on detection of Larmor spin precession of optically pumped atoms, have approached similar levels of sensitivity using large measurement volumes, but have much lower sensitivity in the more compact designs required for magnetic imaging applications. Higher sensitivity and spatial resolution combined with non-cryogenic operation of atomic magnetometers would enable new applications, including the possibility of mapping non-invasively the cortical modules in the brain. Here we describe a new spin-exchange relaxation-free (SERF) atomic magnetometer, and demonstrate magnetic field sensitivity of 0.54 fT Hz(-1/2) with a measurement volume of only 0.3 cm3. Theoretical analysis shows that fundamental sensitivity limits of this device are below 0.01 fT Hz(-1/2). We also demonstrate simple multichannel operation of the magnetometer, and localization of magnetic field sources with a resolution of 2 mm.
磁场是最基本且无处不在的物理可观测量之一，承载着有关所有电磁现象的信息。在过去30年里，工作在4K温度下的超导量子干涉器件（SQUID）作为超高灵敏度磁场探测器一直处于领先地位，其灵敏度可达1 fT Hz^(-1/2)（1 fT = 10^(-15) T）。例如，它们实现了大脑产生磁场的映射以及潜在电活动的定位（脑磁图）。基于光泵浦原子的拉莫尔自旋进动检测的原子磁力计，在使用大测量体积时已接近类似的灵敏度水平，但在磁成像应用所需的更紧凑设计中灵敏度要低得多。原子磁力计若能实现更高的灵敏度和空间分辨率并结合非低温运行，将能开启新的应用，包括无创绘制大脑皮层模块的可能性。在此，我们描述了一种新型的无自旋交换弛豫（SERF）原子磁力计，并展示了其在仅0.3 cm³的测量体积下磁场灵敏度达到0.54 fT Hz^(-1/2)。理论分析表明，该器件的基本灵敏度极限低于0.01 fT Hz^(-1/2)。我们还展示了磁力计简单的多通道操作以及分辨率为2 mm的磁场源定位。
