Spectroscopy has been a central tool in modern physics: it has helped us understand atomic structure, the expansion of the universe and the composition of exoplanet atmospheres. Today, high-precision spectroscopy is one of the most promising tools for investigating questions touching on the most fundamental nature of our universe: What is the nature of dark matter and dark energy, which make up the majority of the universe? What is the cause for the imbalance between matter and antimatter? And how can we combine quantum physics and general relativity? Theorists have proposed answers to these questions which predict changes of fundamental constants over time or space, new interactions and new particles. Many of these candidates for new physics directly influence atomic transition frequencies, which can then be measured in spectroscopy experiments. However, the predicted effects are very small and yet need to be discovered experimentally. Thanks to a steady increase of the precision in atomic spectroscopy measurements, finding the answers to these questions is now coming into reach of table-top atomic physics experiments in an optics laboratory. Highly charged ions have been identified as a system that is especially sensitive to quantities of interest: they can detect two orders of magnitude smaller signals than typical atoms and ions at the same precision. While the level structure and energy regimes of highly charged ions make it difficult to control them directly, methods have been developed to control them indirectly using quantum information tools, via other, easier to control systems such as singly charged ions. The technique to indirectly measure atomic transition frequencies is called quantum logic spectroscopy, and is closely related to quantum logic gates used for quantum computing.
In her new project "AlphaVar", Dr. Vera Schäfer from the Max-Planck-Institut für Kernphysik in Heidelberg wants to pursue these experiments: "With the help of quantum logic spectroscopy, we want to measure two specific transitions in HCIs simultaneously and compare their transition frequencies directly with each other. This method not only increases sensitivity, but also reduces errors introduced by an indirect comparison via the SI second standard" explains Schäfer. This will allow an improvement of over an order of magnitude on current bounds on the temporal variation of the fine-structure constant. "These and other measurements on the new setup will test the predictions of some of the most viable theories for physics beyond the standard model," adds Schäfer.
Dr. Vera Schäfer received her doctorate from the University of Oxford in 2018. After research stays in Oxford and Boulder, Colorado, she has been a Humboldt Fellow and Junior Research Group Leader at the Max Planck Institute for Nuclear Physics in Heidelberg since 2023.
The ERC Starting Grants are among the most prestigious and competitive EU funding programs and support researchers at the beginning of their scientific careers to start their own projects, build their own teams and pursue their most promising ideas. In this year's process, 494 European applications were successfully accepted for funding, with 98 projects going to Germany. A total of almost 780 million euros in research funding was approved. The success rate for the applications is 14.2%.
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