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Optical Magnetometry

Working group 8.21

Optically pumped magnetometers


In an optical magnetometer, atomic spins collectively precess in an ensemble such that their optical properties are magnetic field dependent if the frequency of the laser light is resonant with the atomic transition. The preparation of the atoms with laser light is called optical pumping, hence these quantum sensors are also called optically pumped magnetometers (OPM).

Optically pumped magnetometers (OPMs)

In optically pumped magnetometers, gaseous atoms are used as sensitive magnetic field probes. For this purpose, the quantum-mechanical state of the atoms is prepared by using laser light and the effect of a magnetic field on this state is read out by laser light. During the preparation, the spins of the atoms in a vapor cell are "pumped" into a certain spin state and driven to a coherent rotation. In a magnetic field, the spins then precess collectively with the Lamor frequency which is proportional to the magnetic flux density. This effect on the quantum-mechanical state of the atoms is subsequently read out by means of laser-spectroscopic methods.

OPMs have rapidly developed in the past two decades and now reach sensitivities like those of the superconducting quantum interference devices (SQUIDs) established in biomagnetism. As sensitive medium inside an OPM serve gaseous gaseous atoms; e.g. evaporated alkiali metal atoms as potassium, rubidium or cesium. Therefore, no cryogenic temperatures are necessary and OPMs can ultimately be small and flexible.

The goal of the group is the further development of OPMs to open up new fields of application in clinical neuroscience, medical physics (e.g. detection and imaging of magnetic nanoparticles) and fundamental physics.

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