The core of the nuClock project is formed by eight European groups, which receive funding from the European Union. We seeks to attract more and more scientists into the field of research on Th-229, and to foster communication and synergies among all Thorium groups world-wide. In order to increase the visibility of strong links to partners outside of the project core, we established a group of nuClock associates. We are delighted to be able to collaborate with these great researchers on exciting research projects. nuClock associates are presented here in alphabetical order.
José Crespo, MPIK Heidelberg (Germany)
The group of José Crespo is based at the Max Planck Institute for Nuclear Physics in Heidelberg. It is one of the world’s leading groups in the development of EBITs (Electron Beam Ion Traps). As the name suggests, the space charge of a strong electron beam creates a conservative potential for positively charged ions, irrespective of the ion’s electronic structure, mass, or ionization state. As such, any ion (especially highly charged ions, HCIs) can be trapped in an EBIT. Such traps are of high interest when it comes to the trapping of highly charged Th-229(m) ions. This group also develops cryogenic traps, where technology can be transferred to a cryogenic Paul trap for Th-229(m) to obtain vacuum-limited ion lifetimes on the order of the isomer lifetime. The group of José Crespo is closely linked to the group of Klaus Blaum, who operates high-precision single-ion traps.
Christoph E. Düllmann, GSI & University of Mainz (Germany)
Thorium is a very reactive element that is hard to come by. It is also a refractory element that cannot be evaporated easily. The isotope Th-229, which is the centerpiece of our research, is radioactive and not primordial: it just does not exist on Earth, unless it is produced artificially in nuclear reactors. Once produced, it needs to be separated from other elements, such as uranium, and prepared in a form that can be used in the experiment. While doing so, supreme care has to be taken, as the Th-229 material is scare (only mg amounts are available), expensive (about 50,000,000 USD per gram) and radioactive. This said, it is clear that we want to collaborate with radiochemists that know how to handle such substances. Christoph Düllmann, with various affiliations at GSI and Mainz, is one of these people.
Piet van Duppen, KU Leuven (Belgium)
Piet van Duppen is a member of the Nuclear spectroscopy & Nuclear reactions group at KU Leuven. He recently started a research project on Th-229 and, aside from vast experience in experimental nuclear physics methods, has access to the ISOLDE facility at CERN.
Kerstin Ergenzinger, Berlin (Germany)
Kerstin Ergenzinger is an artist working in the fields of installation, electronic arts/new media and drawing. Her works explore the sensory and conceptual relationships between the individual and its physical surroundings. By focusing on processes of perception, on technologies and strategies applied in spatial and mental navigation and the production of knowledge, she investigates the limits of human perception and our capacity to comprehend and interpret our environment. How do you move in the world, and how does that feel? How does your body relate to other bodies and to its surroundings, and how can you define the coordinates of our own position? In response to these fundamental questions, she develops in her works diverse points of view that play with the opposition between metaphorical distance and physical immediacy. Alongside her studio practice she is frequently involved in collaborative projects and research projects in the fields of dance, music, film and science.
Kerstin Ergenzinger and the nuClock consortium will interface arts and quantum physics. Part of her work will be aligned with the European FEAT initiative; an action that brings together artists and FET projects. The mission of this action is two-fold: First, it seeks to explore how art work can be used as a novel channel to communicate contemporary research to a broad audience. Second, FEAT serves as a broad and open platform to discuss relations between the realms of arts and science from a philosophical point of view. The results of the joint art/science work will be shown at prestigious exhibitions and published in peer-reviewed journals.
Navigating Noise (2015). Photo: Katja Hommel.
Wanderer  (2014). Photo: David Ertl.
Thomas Stöhlker, GSI & University of Jena (Germany)
Thomas Stöhlker is affiliated with the Institute of Optics and Quantum Electronics at the University of Jena, with the Helmholtz Institute Jena, and with GSI in Darmstadt. He works on atomic physics with highly-charged ions. As such, he is used to energies of a few 10 keV, very similar to low-lying excited nuclear states. He has developed X-ray lenses, which can be used to focus radiation of a narrow energy band onto a detector, while defocusing all other photons away from the detector. Such a lens has been made available for the micro-calorimeter development at Heidelberg.
Xiaoyang Wang & Rukang Li, Chinese Academy of Sciences, Beijing (China)
The technologically most advanced way to generate laser light at UV wavelengths is via second-harmonic generation in suitable crystals. The group at the Chinese Academy of Sciences has a long-standing tradition and unparalleled experience in the development of such crystals (LBO, BBO, KBBF). KBBF is the only type of crystal developed so far that fulfills the phase-matching condition down into the VUV wavlength range. A very fruitful collaboration with this group will see the development of narrow-linewidth laser in the VUV.
Atsushi Yamaguchi, RIKEN, Tokyo (Japan)
Atsushi Yamaguchi spent a few years with Ekkehard Peik’s group at PTB, where he performed the first attempt on optical spectroscopy of the Th-229 isomer transition using synchrotron radiation. Afterwards, he moved on to become a member of the famous Katori labs at RIKEN, where he develops and improves optical clocks of the world’s finest standards. Prof. Katori is one of the fathers (if not the father) of optical lattice clocks.
Koji Yoshimura, Okayama University (Japan)
The University of Okayama (about 4 hours south of Tokyo by Shinkansen) accomodates the Research Core for Extreme Quantum World, established in 2013. Part of the research is dedicated to a meausurement of neutrino rest masses using quantum optics techniques. The mechanism of choice is called RENP (radiative emission of a neutrino pair), which makes use of a superradiant coupling between two suitable quantum states. Among a set of various other candidates, the ground and isomeric states of Th-229 are considered as a pair of such quantum states. As with all other experimental groups, a careful analysis of the basic properties of this two-level system is the first priority.
The Okayama group has frequent access to the SPring-8 facility, which prides itself as the largest third-generation synchrotron facility in the world. The storage ring of SPring-8 has a circumfence of almost 1.5 km and holds electrons at an energy of 8 GeV. The beam current is usually 100 mA, operated in top-up mode. There exist some 50 beam lines with a maximum light intensity at photon energies ranging from soft X-rays (100 eV) to hard X-rays (300 keV), where the full available spectrum spans from 12 meV to 3 GeV. Some of the measurements performed here by the Okayama group employ Th-doped crystals produced by the Vienna group.
Friends of nuClock
The scientific work and technology development within nuClock is greatly supported by a number of individuals, companies, and institutes. We are greatful for the support by these friends of our project.
MLS facility in Berlin-Adlershof
The Metrology Light Source (MLS) is a synchrotron facility in Berlin, operated by PTB. The synchrotron runs at electron energies between 100 and 600 MeV and is designed to emit light with a very well-defined intensity, to be used for calibration purposes. The spectrum covers the entire range from the the near-IR down to the VUV range, which is ideal for a broad scan across the anticipated isomer transition in the VUV. First measurement campaigns with Th surface-adsorbed crystals from PTB have already been performed, and future campaigns using Th-doped crystals from TU Wien are currently being prepared.
Jochen Wieser, SME excitech
The Th-229 isomer transition is expected to be located in the VUV wavelength range, somewhere between 120 and 200 nm. Ideally, one would like a strong, continuous-wave (cw), tunable and narrow-linewidth light source for spectroscopy, ideally a laser. Unfortunately, cw lasers below 190 nm are still under development. Other cw light sources include deuterium lamps (which, however, emit only a spectrum of discrete and narrow lines) and synchrotrons. In search for a strong table-top VUV light source with a continuous output spectrum, nuClock collaborates with the SME excitech on the improvement of excimer lamps. Here, a gas is excited to a plasma via an electron beam, and emits continuous radiation in a well-defined spectrum with a width of about 15 nm. The peak position of the spectrum can be tuned by choice of the gas.