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Manuscript on frequency conversion now on arXiv


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 here.

Visit of Mrs Ina Brandes, NRW state minister for science


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 here.

3 open PhD positions


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. Stellmer.

Visiting Wettzell, home of the G-ring gyroscope


Somewhere deep deep in the Bavaria, where villages have funny names and the scenery looks a bit like Canada, only a short hike from the Czech border: that's where you find the world's finest geodetic observatory, the Fundamentalstation Wettzell. Our Gyroscope team certainly enjoys a three-day excursion to learn more about ring-laser gyroscopes, VLBI and all related space geodetic techniques.


Welcome Noah for a summer internship


The latest addition to our team is Noah, who will be with us for a summer internship. Noah joins us from Charlotte (USA) to get a flavor of everyday work in the lab, before embarking on his physics studies in a year from now. Noah will set up servo motors for optical beam shutters for us: Welcome Noah!


New results presented at the Quantum Alliance PhD workshop


We finally got the frequency conversion in high-pressure gases to work! Ali will present the results at this week's workshop of the Quantum Alliance in Munich. Congratulations!


Press release on our QuantERA project QuantumGuide


Prof. Stellmer is coordinator of the QuantERA project QuantumGuide, which will start in July 2022. The press release came out today, check out the German version or the English version.


Virtual DPG meeting in Erlangen


This week is AMO DPG meeting week, and unfortunately it's only virtual. We'll be presenting last year's results in a number of talks and posters: please come and visit us! On Monday afternoon, Simon will give an invited "Hauptvortrag" on our gyroscope project. Looking forward to many discussions!


Two manuscripts accepted for publication


The two manuscripts that we had submitted on the day before Christmas have been accepted for publication: that's Anica's paper on the single-photon frequency conversion (to appear with Optics Letters) and Quentin's paper on the mercury MOT characterization. Congratulation to all co-authors!


ZincClock now a DFG project


The ZincClock project has received funding through the Deutsche Forschungsgemeinschaft (DFG). Funding includes a PhD position as well as all these large and small items that make our work in the lab so enjoyable. Thanks a lot to DFG: we are looking forward to exciting experiments with the new species.


The German Einheitschronometer


Precise timekeeping has always been of particular importance for navigation on the sea. About 100 years ago, German watchmakers joined forces to develop the so-called Deutsches Einheitschronometer, a highly precise mechanical clock that set the standards in naval navigation for 50 years to come. Post-WWII, the Einheitschronometer was built by Wempe in Hamburg for the Western navies, and by the VEB GUB in Glashütte for the Eastern navies. Since the 1970s, mechanic clocks were superceeded by quartz (and more advanced electronic) clocks, but some of the antique Einheitschronometer were salvaged from submarines and other vessels. Prof. Stellmer managed to get hold of one of these devices: the Quantum Metrology group now operates a beautiful 50-year old GUB Einheitschronometer!


Welcome Christian Mielke


With the beginning of this year, Christian Mielke will start his PhD on topics at the interface of geodesy and precision timekeeping. Christian is a thoroughly trained geodesy guy and will be jointly supervised by Jürgen Kusche and Simon Stellmer. He will begin his work by considering a network of clocks placed on the established tidal gauge stations to implement a unified height system via relativistic geodesy.


Wishing everyone a peaceful Holiday season


It's been the second year under COVID-19 rules, but we sure tried to make the best of it. Now that our research will pause for a few days, we wish everyone a joyful Holiday season. All the best for the New Year, let's be optimistic that 2022 will bring back some of the communication habits that we missed this year.


Collaborative work with FZ Jülich now on the arXiv


Quantum dots are nice sources of photons, but their emission wavelength needs to be changed if their photons are to be coupled to atoms or ions, or fed into fiber networks. Here, we show frequency conversion of single photons, emitted from InGa/GaAs quantum dots at 852 nm, to a wavelength of 370 nm that matches to Yb+ ions. The conversion efficiency is sufficiently high (and the background sufficiently low) that we can show the single-photon characteristic of the converted UV photons. This was a true joint initiative with Beata Kardynal's group in Jülich, congratulations to Anica and the teams! Link:


Mercury MOT characterization now on arXiv


We have compiled a long paper that summarized 1.5 years of optimizing our mercury MOT to reach high phase-space densities. Nice work by Quentin and the mercury team:


QuantERA project suggested for funding


The project QuantumGuide has been suggested for funding through the European co-funded QuantERA program. A great success for Prof. Stellmer, who put together the proposal and will coordinate the project. Within this project, we will establish the loading of individual laser-cooled alkaline-earth-metal atoms (e.g. Ca or Sr) through hollow-core photonic crystal fibers to feed quantum sensors and ion-based quantum computers. The consortium also includes TU Darmstadt, PSI in Switzerland, the University of Torun in Poland, and the company AQT in Innsbruck, Austria. The project will run for three years.


Pre-Christmas gifts


Santa Claus came along and delivered a few parcels. One of them came from Munich, and Thorsten and Lara enjoyed unpacking a new cavity. The other one is from Scotland and contains a frequency-doubled Ti:Sapphire laser, which David and Marc finally set into operation.


UV laser development published with Optics Applied


Our paper on the development of a widely tunable laser near 310 nm has been published with Optics Applied. Congratulations to Maya and the team! Link to the paper:, or on the arXiv:


Two new group members


We welcome two new group members! Alireza Aghababaei did his master thesis with Stefan Linden and now joins our team for a PhD thesis. He will work on the quantum frequency conversion topic within the ML4Q Cluster.

At the beginning of October, Lara Becker will begin her master thesis with us: she will set up a calcium beam clock, which will then become part of our Advanced Lab Course.

Welcome Alireza and Lara, good luck with your research!


Ring laser gyroscope now part of the Advanced Lab Course


During his master thesis work, Cedric Wind set up a passive ring laser gyroscope as a pilot study for our highly precise gyroscopes to be used in geodesy. Starting now, this setup is used within the Advanced Lab Course. It is the first such experiment offered by our group.


Workshop on time and frequency dissemination in mid-September


Within the CLONETS collaboration, we are framing a design report for a future European network for time and frequency dissemination to major research institutions. We are organizing a workshop in Bad Honnef, September 13 to 15. Participation is by invitation only, so if you want to be part of it, send an email to Simon.


Fulbright-Cottrell Award


Simon received this year's Fulbright-Cottrell Award for excellence and innovation in teaching! This award is presented annually by the US/German Fulbright foundation to one male and one female researcher from physics, chemistry, or astronomy. The press release can be found here:


ML4Q OpenCall


The ML4Q Cluster granted us the budget to set up laser systems at 214 nm, which we need for laser cooling of our zinc atoms. It's nice to be part of a Cluster of Excellence...


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