Geodesy and metrology with a transportable optical clock

The development of optical clocks that can be transported and operated outside metrology laboratories promises exciting new and competitive measurement methods for geodesy, where chronometric levelling is considered as a complementary method to measure height differences [1-4].
To perform such tasks in a competitive way, it is not sufficient to demonstrate the clock performance in the laboratory, but transportable clocks need to show reproducibility of their frequency at the level of few parts in 10¹⁷ and better in the various locations to which they are transported and where they are used.
At Physikalisch-Technische Bundesanstalt (PTB), we have developed such a transportable optical clock [5] that has been tested for the applications described above by measurement campaigns outside the laboratory. I will present results of the measurement campaigns we have performed so far and discuss the perspective of our apparatus for chronometric levelling.

[1] A. Ludlow, Nature Phys. 14, 432-432 (2018)
[2] T. Mehlstäubler et al., Rep. Prog. Phys 81, 064401 (2018)
[3] J. Grotti et al., Nature Phys. 14, 437 (2018)
[4] H. Denker et al., J. Geod. 92, 487 (2018)
[5] S. B. Koller et al., Phys. Rev. Lett. 118, 073601 (2017)