News

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 Meeting⁵ 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 technology⁶ 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.

The end of a busy week: Stefan Gessler finished and successfully defended his bachelor's thesis, congratulations! Thomas Gereons finished his internship, only to continue next week on his master's thesis project. Also, three 10th grade high school students spent the week with us: Marie, Karl, and Jonathan explored the capabilities of small Arduino boards, asking ChatGPT to generate the code required to drive small servo motors.

Anica went into mass production mode: while the previous paper has been published with Optics Letters⁷, the next one is already on the arXiv⁸. Both papers study frequency conversion in gas-filled hollow-core fibers in different regimes. Congratulations to Anica! 

With the help of Andreas Brotzer from LMU, we installed a state-of-the-art broadband seismometer in our basement. Side-by-side with our own narrowband seismometer, our tiltmeter, and the large ring laser, we embarked on a three-week measurement campaign during the Christmas break. Indeed, we were able to record a number of teleseismic events (= earthquakes on the other side of the globe) with magnitudes between M6.5 and M7. Thanks a lot to Andreas and the entire team at the Geodetic Observatory in Fürstenfeld-Bruck, as well as to Heiner Igel's group at LMU, for loan of the equipment and for support in data analysis. 

Happy New Year to all of you, hoping for a peaceful and successful year 2025! We are welcoming two new additions to the team: Thomas Gereons started his master internship with us, and Tessa Koch dived into her Bachelor's thesis: good luck to the two of you!

Ring lasers are interferometers that require length stability at a fraction of the wavelength: not a mean feat for heterolithic structures of more than 10 meter length, especially when operated in a wobbling University building with sizeable temperature fluctuations. In a new preprint⁹, Jannik Zenner presents two methods to stabilize the length of the 14-meter ring cavity to within a few nanometers. Congratulations to Jannik and the team! 

It's the beginning of the new teaching term, and we welcome a range of new group members: Vedang Sumbre starts his master thesis on the zinc project, where he will begin with spectroscopy on the 308-nm transition. Darius Hoyer comes in for an internship project, in which he will design the Sr MOT vacuum chamber and optics layout. Last but not last, Stefan Gessler will equip our tiltmeter with a new temperature stabilization enclosure. Good luck to all of you! 

Two new publications from the group: At first, our paper on isotope shifts of the 423-nm transition in calcium recently appeared with Phys. Rev. A¹⁰. Secondly, we performed a systematic study of dust contamination in a quantum optics lab and derived practical recommendations. The manuscript, written by Bachelor student Jonas Gottschalk, is now available on the arXiv¹¹.

Hybrid quantum information networks will require photonic components that can change the color of a photon while leaving the fragile qubit information untouched. The trick is called quantum frequency conversion, and it's an old trick that has been around for a decade or two. In her recent work, Anica played a couple of new tricks: she used gases instead of crystals (crystals are nice but demanding, whereas gases are cheap and easy to handle), she played the trick inside a hollow core fiber, and she used cw light instead of pulsed light to preserve temporal coherence of the photon. All of this became possible through a collaboration with the Max-Planck-Institute for the Science of Light in Erlangen, which provided the fiber (thanks, Michael!), and through the support of Thorsten Peters from TU Darmstadt (thanks, Thorsten!). The manuscript is now available on the arXiv here¹².

While we all took a few weeks of during the summer, we also used the quiet weeks to push on some of our projects. At first, Philipp finished his Bachelor thesis on the 3D ring laser project: congratulation Philipp! Second, Maanas Kishorekumar Bysani from Imperial College London spent an 10-week internship with us. Maanas set up the optics and electronics packages of a future transportable strontium MOT... stay tuned! Lastly, Simon and Jannik shuttled back and forth to the ROMY observatory near Munich to install new electronics on their ring lasers.

The University of Bonn and the state of NRW jointly operate a geodetic observatory near Todenfeld, a beautiful Eifel village about 30 km east of Bonn. The observatory hosts a range of seismometers and, since two years, one of the world's finest superconducting gravimeters. The gravimeter is operated by our colleagues and friends Jürgen Kusche and Basem Elsaka from the Geodesy Institute just across the street and can measure changes in the Earth's gavitational potential at the level of one in a billion. We now installed a commercial fiber-optic gyroscope right next to the gravimeter as a test system for our home-built ring lasers. Already now, we can sense slow changes in rotation at the level of a few 10 nrad per second, that's about one revolution per year. Both the gravimeter and the gyroscope are sensitive to tilt, which might become our next joined project. Thanks to Jürgen and Basem for hosting us!

Lukas Möller has been with us for almost two years already, first as an internship student and then as a master student. Climbing up the ladder, he now started his PhD thesis with us on the Zinc project. Good luck, Lukas! At the same time, Katrin Schatzmayr began her master thesis work on our ML4Q project, aiming to finally add some quantum to our frequency conversion setups. Enjoy your work!

We are entering a new era in terms of laser technology, as we are gradually replacing our Ti:Saphs and tapered amplifiers by VECSEL lasers. The first unit was delivered and installed today (8 watts at 940 nm), three more will follow until the end of the year. Thanks a lot to J-P, Eero, and the entire team at Vexlum for great support!

It's the beginning of the spring season, and we welcome a number of new group members: Felix Waldherr joins us from Heidelberg, he will set up a laser system at 254 nm for the mercury co-magnetometer used at ILL in Grenoble to set new limits on the neutron EDM. Philipp Stürmer joins us for his Bachelor thesis on the 3D passive gyroscope. Priyanka Yashwantrao, who worked with us on the quantum frequency conversion project for the past 1.5 years, starts an external master thesis with our dear friend Tommaso Calarco in Jülich. And last but not least, Frederik Wenger returns from his Bachelor to continue working with us on spectroscopy of the calcium clock transition. Good luck to all of you!

Congratulations to Frederik für submitting his Bachelor's thesis today! Frederik worked on isotope-shift spectroscopy on the 423-nm transition in calcium, where he and the team reached impressively low uncertainties. After a few months in the windowless lab, Frederik will now dive into a work&travel experience down under before returning for the Master's program. Enjoy!

We are celebrating the inauguration of our three ring laser gyroscopes! On Thursday (01.02.2024) after lunch, we'll start with the Geodetic Colloquium at the geodesy department, then move over to the FTD building for a small symposium. At 5 pm, we'll have the inauguration in our labs, followed by lab tours and dinner. More than 20 international guests have confirmed their attendance: we're looking forward to a joyful ceremony. Everyone from the physics and geodesy departments is invited to join! The program can be found here¹³.

Frequency conversion of individual photons is a necessity for many concepts of large-scale quantum information, and conversion to the telecom bands is of particular relevance. However, most approaches employ nonlinear media with a very small spectral bandwidth. Here, we present a scheme that allows for conversion to the telecom bands over a very very wide wavelength range. This work just appeared with Optics Letters and can be found here¹⁴. Congratulations to Anica and the team!

Developing deep-UV lasers might be a challenge, but using them for spectroscopy can be rewarding. Together with dear colleagues from Berlin, we have developed laser systems near 214 nm and demonstrated their performance through spectroscopy on a cryogenic beam of zinc atoms. Congratulations to first author David Röser and the team! The paper can be found here¹⁵.

Hans Keßler joined our team as a senior scientist! Hans previously worked in Hamburg with Andreas Hemmerich on cold atoms coupled to optical resonators. He now moved to the Rhineland region to strengthen the EIN Quantum NRW initiative especially in the area of teaching and education. Welcome Hans, we are glad to have you with us!

It's the beginning of the winter semester, and we are delighted to welcome some new and some well-known faces. At first, Lukas Möller successfully finished his master thesis (Congratulations!) and will stay with the Calcium experiment for a while. Second, Sascha Heider finished his internship on the Gyroscope project and will continue as a master student on the Mercury machine, while Sahil Ugale took over the internship position at the Gyroscope project. Last but not least, Frederik Wenger started his bachelor thesis work on the Calcium experiment. Good luck to the four of you!

Congratulations to Jonas and John for handing in their master theses! Jonas set up the hardware to import and save environmental parameters that are relevant to our gyroscopes: our dust contamination log is now referenced to the GPS signal! John advanced our three-dimensional passive gyroscope through new locking technology. Both Jonas and John will stay with us and work on the gyroscopes.

We are welcoming two new team members. Andreas Reuß joins us after a master thesis with Stefan Linden and will now be leading the Calcium experiment. Sascha Heider will do a summer internship with us and continue as a master student in the fall. Welcome Andreas and Sascha!

The Quantum Metrology research group offers six exciting master thesis projects. These projects span a wide range between laser development, precision measurements, quantum information, and outreach activities and cut across atomic physics, optics, and electronics. Find out more¹⁷

Prof. Dr. Simon Stellmer has been awarded a Proof of Concept Grant by the European Research Council (ERC) as part of a program designed to help researchers translate their ideas from previous ERC projects into commercial applications. The grant is endowed with €150,000. Find out more¹⁸

Mahdi did his Bachelor thesis work on the Quantum Freuency Conversion project and just handed in his thesis. Say good bye to the dark lab, welcome back to the lecture hall!

Today, John Gutsche joined the Gyroscope team to do his Bachelor thesis with us. John will set up a tetrahedral 3D passive ring laser gyroscope, likely the world’s first of this kind. Good luck with your work!

Apart from a range of open PhD and PostDoc positions, we can offer a permanent researcher position. Candidates should contact Prof. Stellmer, please find the job posting here¹⁹, deadline is May 5.

Spring time is DFG meeting time! Anica, Lukas, Thorsten, and Ali went to Hannover to present our research in a number of talks and posters.

Julian is the first-ever Bachelor student in our group, and it seems he did not only survive his stay with us, but he also enjoyed it. Julian set up the heterolithic tetrahedral gyroscope, a massive steel construction that will last a long time. Congratulations Julian!

Highlight of the year! Together with Ulli Schreiber from Wettzell and Andreas Brotzer from LMU Munich, we installed the GeoSensor ring laser gyroscope in our underground lab. This 4-by-4 meter device was previously installed at a geodetic observatory in the desert of Nevada, dismantled there, and re-configured in our lab. We are grateful for this amazing collaboration.

Priyanka recently came to Bonn as a BCGS student for her master studies. She joins the Quantum Frequency Conversion team to explore frequency conversion in high-pressure hydrogen. Welcome Priyanka!

The European UVQuanT project has officially started! This week's kick-off meeting in Berlin will see a gathering of all partners, as well es guests from academia and industry alike. The goal of this 4-year project is an improvement in the reliability of UV lasers and optics, with a focus on the wavelength range between 200 and 230 nm.

Congratulations to Lara Becker and Marc Vöhringer Carrera for having submitted their master theses! Lara worked on the setup of a calcium beam clock, while Marc worked on spectroscopy of Zinc using transitions deep in the ultraviolet. Good luck for your next career steps!

The beginning of the winter term often marks the beginning of a bachelor or master thesis. This year, three students join the group: Lukas Möller (who already did his summer internship with us) will do his master thesis work on the Calcium project, Julian Spanier will do his bachelor thesis in the gyroscope project, and Mahdi Razavi Tabar will start his bachelor thesis on quantum frequency conversion.

Frequency conversion often employs a nonlinear crystal, especially if it comes to conversion processes at the single-photon level. However, crystals come with a certain set of material properties, some of which are good (e.g. large nonlinearities) and some of which are bad (e.g. absorption and phase matching conditions). As an alternative approach, we employ a dense gas of diatomic molecules (hydrogen in this case) as the nonlinear medium. We demonstrate frequency upconversion, downconversion, and show that polarization is conserved: check out the manuscript on the arXiv here²⁰.

Since a couple of weeks, the state of NRW has its new state government (Landesregierung). Today, the new minister for culture and science (MKW), Mrs Ina Brandes, paid her inaugural visit to the University of Bonn to learn about our various excellence initiatives. Simon Stellmer gave a brief introduction to our beloved research topics... optical clocks, gyroscopes, quantum computing, and so forth. We are looking forward to jointly promote research and science in NRW! See the press release here²¹.

We are hiring! Currently, we can offer three PhD positions with our mercury and zinc projects. The mercury project is our oldest and largest experiment, devoted to searches for physics beyond the standard model with ultracold mercury atoms, with a side project on quantum simulation. This project is funded through the ERC, the SFB OSCAR, and the EU project UVQuanT. Within the zinc project, we will develop a novel optical clock based on zinc, and aim to study entanglement and decoherence processes of single atoms trapped in optical tweezers. This project is funded through various DFG grants and is part of the ML4Q Cluster of Excellence. For all of these positions, some experience in a cold atom or laser lab is certainly a bonus. Please enquire with Prof. Stellmer²².