We welcome Sophia to our team! Sophia joins us as an internship student over the winter to get some hands-on experience in atomic physics and work in the optics lab. She will look into somewhat exotic spectroscopy in strontium (3P2 - 3P2, heaven forbid!) before embarking on her master's thesis. Good luck with your work! 

Darius was tasked to build a lovely-looking, transportable and reasonable stable MOT of strontium, and that's what he did as his master thesis project. As part of the EIN Quantum NRW network, we are not proud to have a brightly glowing Sr MOT available for outreach and education purposes in schools and exhibitions. The system runs on a battery and can be pushed around... and yes, the MOT stays on as you are rattling across the parking lot 🙂 Darius will continue as a PhD student with our partner group (Sebastian Hofferberth) in the building next door. 

In a decade-long partnership with the physics community at the University of Canterbury in Christchurch, New Zealand, various ring lasers of different sizes have been built in both the lab and in unterground caverns. Among these, the so-called C-II ring stands out as a 1-square-meter monolithic ring laser of supreme sensitivity and stability. In the mid term, this ring shall be upgraded from purely active operation to hybrid active/passive operation. To this end, Jannik and Thomas spend three weeks down there to implement the passive operation mode. 

Together with many many partners, among them the ExCluster ML4Q, the state-funded network EIN Quantum NRW, the University, and all research groups from the IAP institute, we put together the Quantum To Go exhibition in the city center of Bonn: an exhibition for the lay audience, stretching from Schrödinger all the way to quantum computers, one minute walking distance away from the train station. The program was stuffed with lectures, panel discussions and even concerts, and attracted countless visitors, all the way from tourists to school classes. After six intense weeks, the exhibition is now closed. Thanks to all who contributed to the success, especially to Ecem who took care of the organization! Link: https://www.uni-bonn.de/de/neues/157-2025.

Within the zoo of elements in the periodic table, those with two valence electrons and a J = 0 ground state currently receive a lot of attention, as these are the ones of interest for optical clocks, neutral-atom quantum computing and precision spectroscopy. Among this family of elements, zinc has received only little attention. Driven by our recent advances in the development of UV laser technology, we were able to present the world's first laser cooling of zinc. Lukas wrote a manuscript that is now available on the arXiv: https://arxiv.org/pdf/2510.21376. 

High-precision isotope shifts may open a window to nuclear physics and to searches for physics beyond the standard model. With a wealth of research currently going on world-wide, we are adding our small contribution to the large puzzle by interpreting spectroscopic data on three different optical transitions. Three years of work in the lab and data analysis squeezed into a four-page manuscript: congratulations to Thorsten and the team: https://arxiv.org/pdf/2510.18514. 

The most common technique to stabilize a laser to a reference cavity is Pound-Drever-Hall locking, but a phenomenon called residual amplitude modulation (RAM) leads to small but annoying frequency drifts. Hänsch-Couillaud locking, on the other hand, does not require RF sidebands, but in turn relies on polarization, which tends to drift as well. Here, we present Hänsch-Couillaud locking of our 14-meter ring cavity. Flicker noise sets in quite quickly, by adding a lock-in detection allows us to gain almost an order of magnitude in sensitivity. Jannik wrote a short manuscript that can be found on the arXiv: https://arxiv.org/pdf/2510.08183. 

Johanna did her bachelor thesis with us, working on the characterization of an atomic beam. Now that the thesis is submitted and defended, she'll return to the lecture hall for her master studies: good luck! 

Welcome Felix, who re-joins our group for his PhD thesis. Felix studied in Heidelberg and already did an external master thesis with us, setting up the xenon two-photon spectroscopy experiment. After a short break, he now continues as a PhD student on the zinc experiment. Good luck with your work! 

Georg Enzian joins the group as permanent staff! Georg has studied here in Bonn before starting a PhD in Oxford on cavity optomechanics. He then moved on to Copenhagen and further on to a quantum computing company. Georg brings in a wealth of experience, and we are very glad to have him: welcome to the team! 

In the vicinity of Munich, LMU operates a unique observatory: an underground array of four ring lasers, arranged to the shape of a tetrahedron with a side length of 12 meters. The project is calles ROMY, which stands for ROtational Motions in seismologY. We are proud to contribute measurement technology and expertise to ROMY, and a careful characterization of the device has just been published with Review of Scientific Instruments (link: https://doi.org/10.1063/5.0242127). 

Work around the extended Pentecost weekend has been quite successful: Anica's most recent paper on basic properties of frequency conversion in dense gases has been accepted by Optics Letters (DOI: 10.1364/OL.553732). We also have two new manuscripts on the arXiv: One is on our endeavour to generate 100+ mW of light at 213 nm (https://arxiv.org/abs/2506.08709), the other one on the latest improvements in our frequency conversion business (https://arxiv.org/abs/2506.05989). Enjoy reading them!

A dream comes true: all three Cluster applications of the physics department were successful and will now be funded for at least seven years. Apart from ML4Q, this includes the Color meets Flavor (CmF) initiative of our colleagues from high energy physics, as well as the Dynaverse initiative from our astronomy fellows. Coming back to quantum physics, also all existing Clusters of the Quantum Alliance were continued: a great success of both our department and our field of research. Congratulations to all winners, we are looking forward to another 7 years of intense work.

Two member of the Quantum Metrology team finished their theses: Tessa learned how to operate an active ring laser in a passive fashion: still some instabilities, but it's the first hybrid ring laser, world-wide: congratulations! Felix joined us from Heidelberg and worked on two-photon spectroscopy of a deep-UV transition in Xenon: now he can call himself a master of science! 

It's the end of the winter break and the beginning of the summer term, and there has been some shuffling within the team. Katrin and Priyanka finish their master theses: Katrin worked in the frequency conversion, while Priyanka had worked with us previously and now did a master thesis with our beloved friend Tommaso Calarco in Jülich. Benny joined us from Heidelberg for part of his master thesis on xenon spectroscopy, and Johanna will join us for her bachelor thesis on the Sr MOT experiment. And we welcome back Sascha, who officially begins his PhD thesis on the mercury experiment. All the best to all of you! 

Time passes quickly: we are celebrating already the 7th birthday of our research group. What started in April 2018 with no labs and no offices has grown into a vibrant team of nearly 20 people operating eight full-fledged optics labs. Sadly, it's also the end of the quMercury ERC project, which went through two extensions and shaped the first seven years of our group. But no worries, the quMercury project made it into the community input for the European Strategy for Particle Physics Update!

We'll have the DPG Spring Meeting coming up next week, with around 1600 AMO folks coming to Bonn. We will be contributing 6 talks and 7 posters, so watch out for the Quantum Metrology logo! We will offer lab tours on Tuesday, Wednesday, and Thursday at 2 pm and 5 pm, starting from the main entrance of the Physics Institute at Nussallee 12. Get in touch with us if you want to see the labs and learn more about our work. A big THANK YOU goes to Sebastian Hofferberth an his team for organizing the conference. 

In German, there is a saying "Am Aschermittwoch ist alles vorbei", which might be translated as "Everything ends on Ash Wednesday". Keeping with this saying, David Röser had his PhD defense today (Ash Wednesday!) to finish his PhD thesis not in ashes, but with a large celebration on a beautiful sunny day. The title of his thesis reads "Spectroscopy and the Path to Laser Cooling of Zinc", and David indeed developed a range of components and procedures that form the foundation of our Zinc experiment. Congratulations, Dr. Röser! 

Here it is: our first publication on ring laser technology has been published with Optics Letters! Jannik set up two schemes to lock the free spectral range of GeoRG, our largest ring laser with an arm length of 3.5 meters. A simple phase lock is sufficient to keep the perimeter length constant to within 5 nanometers.