Spectroscopy of laser cooled atoms and ions has enabled the investigation of isolated matter with astonishing precision, culminating in the realization of optical frequency standards, that demonstrated metrology at the 18th digit for the first time. However, the crucial techniques for these measurements, namely laser cooling and fluorescence detection require suitable electronic transitions that are not present in most atomic and nearly all molecular species.
For spectroscopy of on the clock transition of Al+ this issue has been solved by the classical quantum logic spectroscopy (QLS) protocol, making the 1P0 to 3P0 clock transition accessible for metrology.
The focus of this project is to extend the classical QLS protocol to even more complex species such as molecular ions. The challenges in such systems are the presence of multiple metastable ground states with super-GHz energy spacing and the absence of narrow transitions for the traditional implementation of QLS.
Our main focus lies on the development of a quantum logic toolbox for the investigation of molecular ions. This toolbox will involve efficient techniques for state preparation and detection. The first step has already been achieved by realizing the first demonstration of non-destructive rotational state detection for a molecular ion .
The long term goal is to push the limit of achievable accuracies from 10-9  towards the performance of today’s optical frequency standards [3,4]. Accuracies on this level would allow to explore new physics by setting bounds, orders of magnitude more stringent for theories beyond the standard model, which involve variation of fundamental constants or an electron electric dipole moment larger than predicted by the standard model.
Furthermore, we develop and test technical equipment for the laser manipulation of Mg ions, such as optical fibers for the UV range.
 F. Wolf et al., Non-destructive state detection for quantum logic spectroscopy of molecular ions. Nature, advance online publication (2016). www.nature.com/nature/journal/vaop/ncurrent/full/nature16513.html.
 J. Biesheuvel et al., Probing QED and fundamental constants through laser spectroscopy of vibrational transitions in HD+ , Nature Communications 7,10385 (2016)
 T.L. Nicholson et al., Systematic evaluation of an atomic clock at 2 × 10−18 total uncertainty, Nature Communications 6, 6896
 N.Huntemann et al. Single-Ion Atomic Clock with 3×10−18 Systematic Uncertainty, Phys. Rev. Lett. 116, 063001 (2016)
Jan Christoph Heip, Fabian Wolf, Chunyan Shi, Piet O. Schmidt
Florian Gebert, Yong Wan, Börge Hemmerling