Atomic magnetometer

An atomic magnetometer measures magnetic fields by detecting how the field changes the spin states of atoms, often in a vapor cell.

Larmor precession: The rotation of a magnetic moment around an applied magnetic field at a field-dependent frequency. Its frequency provides a direct measure of magnetic-field strength.
Electron spin: An intrinsic quantum property of electrons that gives them angular momentum and a magnetic moment. Electron spin supplies much of the magnetic response measured in alkali-vapor sensors.
Magnetoencephalography: A brain-imaging method that maps magnetic fields generated by neuronal activity. Wearable optically pumped sensors can measure brain fields without superconducting detectors.
SQUID: A superconducting device that detects magnetic flux through changes in current or voltage in a superconducting loop. SQUIDs are highly sensitive but generally require cryogenic cooling, unlike many atomic sensors.
Alfred Kastler: A French physicist who developed optical pumping and received the 1966 Nobel Prize in Physics. His optical-pumping method provided a key way to prepare atomic spins for magnetometry.
Faraday effect: The rotation of a light wave’s polarization as it passes through a medium in a magnetic field. Polarization rotation can reveal the spin polarization of atoms in optical magnetometers.
Nuclear spin: An intrinsic angular momentum of an atomic nucleus that produces a nuclear magnetic moment. Nuclear spin can contribute to the signal and relaxation dynamics of some atomic sensors.
Magnetocardiography: The measurement and mapping of magnetic fields produced by electrical activity in the heart. Atomic sensors can detect cardiac magnetic signals without placing electrodes on the skin.
Fluxgate magnetometer: A magnetic-field sensor that uses the nonlinear response of a magnetically permeable core driven by alternating fields. Fluxgates are robust and practical, but generally less sensitive than precision atomic devices.
Optical pumping: A process that uses light to redistribute atoms among internal energy states. Its development established the central preparation technique used in many atomic magnetometers.

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