In relativistic geodesy, frequencies of distant optical clocks are compared to measure the relativistic redshift and thereby the geodetic height difference between the clocks. To obtain a height resolution of on the order of 1 cm, clocks with a fractional frequency uncertainty of 10-18 are required.
Here, we present a joint effort between PTB and DLR-SI to build a transportable aluminum ion clock. In contrast to other species, the aluminum clock transition is very insensitive to blackbody radiation. The linear and quadratic Zeeman shifts are small, and the electric quadrupole shift is negligible. These favorable features led to the first optical clock with an estimated systematic uncertainty below 10-18 . However, a co-trapped so-called logic ion is required for sympathetic cooling and state readout via quantum logic spectroscopy .
The transportable clock setup benefits from our experience gained during development of a similar laboratory clock apparatus with a preliminary estimated apparatus-related systematic fractional frequency uncertainty of 1.9x10-18 . Other key-components are a segmented multi-layer trap made of AlN substrates , a transportable reference cavity for the clock laser , and a single-pass fourth harmonic generation unit for the clock laser that facilitates an uninterrupted phase stabilization of the fundamental laser.
We present preliminary characterization results of the reference cavity and the FHG unit as key building blocks of the clock laser. Moreover, we present potential applications of such clocks for geodetic measurement campaigns.
 S. Brewer et al., “27Al+ Quantum-Logic Clock with a Systematic Uncertainty below 10−18” Phys. Rev. Lett. 123 (3 2019), p. 033201
 P.O. Schmidt et al., “Spectroscopy Using Quantum Logic.” Science 309.5735 (2005), pp. 749-752
 S. Hannig et al. (2019), “Towards a transportable aluminium ion quantum logic optical clock”, Rev. Sci. Instrum. 90, 053204
 T. Burgermeister (2019), “Development and characterization of a linear ion trap for an improved optical clock performance”. Phd thesis, Leibniz Universität Hannover.
 S. Herbers (2021), “Transportable ultra-stable laser system with an instability down to 10−16“. Phd thesis, Leibniz Universität Hannover.
|Presenter name||Stephan Hannig|
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