Under an ERC Advanced Grant, we perform precision spectroscopy of the simplest molecule. We compare the transition frequencies with theoretical predictions. This opens up important topics: the determination of fundamental constants, a test of the wave properties of quantum matter, a search for exotic forces, so-called o"fifth forces". For more information, see Alighanbari et al 2020 and Kortunov et al 2021. In the framework of the project we also develope new techniques for spectroscopy of ions in traps.
In collaboration with our partners Dr. C. Lisdat (PTB Braunschweig) and Prof. K. Bongs (U. Birmingham), we have developed a transportable optical atomic clock based on ultracold strontium atoms [Origlia et al 2018]. It is currently undergoing an upgrade, with an improved clock laser, a transportable Ti:Sapphire lattice laser, and a transportable frequency comb. We intend to operate the clock in the near future at the fundamental station Wettzell (collaboration with Prof. U. Schreiber, TUM) and to exchange time signals with the ISS experiment ACES.
In a second project we are developing a transportable ytterbium lattice clock.
These projects will profit from technology developments we are pursuing in the framework of a BMBF-funded consortium called "ISABELLA" (coordinator: Dr. Sacher, Sacher Lasertechnik GmbH).
We search for temporal oscillations of fundamental constants with spectroscopic experiments. Such oscillations are a conceivable consequence of a quantum mechanical field of dark matter parts. In cooperation with the University of Mainz we demonstrated a molecular spectroscopy approach [Oswald et al - arxiv].
An optical resonator can be produced from a block of matter with suitable physical properties (e.g. stifness, thermal conductivity, thermal expansion coefficient, dimensional stability), in particular from a crystal, and two attached juxtaposed mirrors. To monitor the dimensional stability of a resonator a laser wave can be resonantly coupled into it. From a modern point of view, the comparison of the frequency defined by the macroscopic optical resonator and the frequency of a microscopic (quantum) standard (an atomic clock) provides an approach for searching for signatures of hypothetical time variations of fundamental constants, of the expansion of the universe, of a violation of the equivalence principle of relativity and of the interaction between conventional matter and dark matter.
We pioneered the field of cryogenic optical resonators and have a long-standing program aimed at studying the properties of such resonators and using them for fundamental physics tests. Our recent line of work are resonators fabricated from near-perfect silicon crystals and operated at 1.5 Kelvin continuously for months to years. Extremely low long-term drift of the resonator frequency has been found under these conditions. We are working on improving the resonator's short-term performance, in particular by implementing a cryogenic vibration isolation system and will perform new tests of fundamental physics.