Optical Frequency Metrology

The advances in quantum engineering have enabled frequency metrology with unprecedented accuracy, allowing us to determine frequencies with a relative uncertainty of below one part in 10¹⁸. This accuracy makes it possible to precisely detect differences in the terrestrial geopotential through gravitational redshift in a clock comparison. State of the art laboratory optical clocks have reached measurement resolutions corresponding to a height difference in the geopotential of 1 cm on Earth, outperforming classical geodetic techniques. This sparks discussions of a new access to the geoid and the precise linking of physical height systems over very large distances and paves the ground for a novel height reference system based on optical clocks that is more stable, reproducible, global, and maintainable compared to todays employed approaches. The additional information provided by optical clocks will revolutionize our understanding of Earth, including societally relevant phenomena such as sea level rise, ice-mass loss, post glacial rebound, mass balance and much more, in particular when combined with data from quantum gravimeters.

The department Optical Frequency Metrology develops optical clocks for their operation on Earth and in space. This development specifically targets a reduction of the size, improved energy efficiency and robustness, temperature insensitivity, and self-sustained operation. For example, the project InnoVaQ aims at the integration of a vacuum system with an atomic source in a compact setup as a core component for future compact optical clocks.