Atom-based quantum sensing of electromagnetic fields

The spin and electronic degrees of freedom in atomic systems provide sensitive and versatile means for detecting electromagnetic fields, from DC to THz frequencies, with spatial resolutions ranging from the nanoscale to meter scale. Such sensors offer unique advantages compared to classical approaches, resulting from their intrinsic quantum nature. We review three different sensor modalities: atomic vapor magnetometers, nitrogen-vacancy-center magnetometers, and radio-frequency sensors based on Rydberg atoms. We emphasize the unique features and capabilities of these types of sensors in the context of real-world applications.