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Research projects in our group



"Quantum metrology": that's the art of measuring using phenomena from quantum physics. Specifically, we aim to increase measurement sensitivity beyond of what would be possible in classical systems, and we do this in an interdisciplinary approach.

We cover a broad range of topics, spanning from very fundamental questions ("Why is there only so little anti-matter in the Universe?") to the develpment of devices very close to applications (such as photonic modules for future quantum communication). And as we all know, optical clocks are by far the most precise measurement instruments we can think of, so we put in some effort to improve them further.


Our research is structured into six different projects: 


The quMercury project: Quantum gases for a measurement of the atomic EDM of mercury



The Universe contains substantially more matter than antimatter. What is the reason for this imbalance, why does Nature favor matter over antimatter? This is one of the most challenging problems in fundamental physics, and we are taking a new approach to tackle this problem. The matter/antimatter imbalance is connected to a quantity named electric dipole moment (EDM): a small deformation of the charge distribution of fundamental particles. The current best measurements of this EDM have been performed with gases of mercury atoms at room temperature.

Now, we will take this experiment to the quantum world: we will prepare quantum-degenerate Fermi gases of mercury as the basis of our measurements, which shall improve measurement sensitivity by two orders of magnitude. Ultracold samples of mercury have not yet been studied, so the preparation of Bose-Einstein Condensates (BECs) and Degenerate Fermi Gases is the first step along this road. These systems can also be employed as platforms for novel schemes of quantum simulation and hold the potential to improve the world’s best optical clocks. All of the cooling transitions in mercury are in the UV range 185 and 254 nm), where quite a bit of development in laser technology will be required.

Welcome to the challenge of setting up one of the world’s leading experiments for quantum simulations and EDM measurements! 


The ZincClock project: Exploring zinc as a new candidate for optical clocks

Many different atomic species are currently under investigation for optical clocks. Each of them has its advantages and disadvantages, and it is not clear yet which element will, in the long run, be the most suitable choice for the most precise, accurate, robust, cheapest, or simply "best" optical clock. We believe that the element zinc has all the properties it takes for a competitive clock: a very broad singlet cooling transition for a fast and efficient first cooling stage, a narrow (4 kHz) triplet transition for a second cooling stage, and a very low sensitivity to black-body radiation. Most of the wavelengths required for cooling and clock operation can be derived as higher harmonics from telecom wavelengths, which simplifies the laser systems and might ease market integration.

So far, optical spectroscopy (let alone laser cooling) of Zinc have not been performed. In this project, we are setting up a lattice clock experiment to perform laser cooling of zinc, and to investigate its basic properties.





The CalciumClock project: Robust clocks for application outside the lab

03_Logo_CalciumClock_rgb.pngThe world’s finest optical clocks reach a stunning fractional uncertainty in the 10-19 range: they would be off by less than a millisecond when operated over the age of the Universe. Equally impressive, they are sensitive to the gravitational redshift in the Earth’s gravitational field that corresponds to a height difference of about 1 cm.

The usage of these dedicated optical clocks with a performance in the 10-19 range is certainly limited to very few metrology labs. For industrial applications (e.g. timekeeping or synchronization of networks), a performance comparable to hydrogen masers (fractional uncertainty in the 10-16 range) would be sufficient.

In this project, we aim to develop rugged and small optical clocks with an uncertainty in the 10-16 range, to be employed outside a quantum optics laboratory. A number of such clocks will be connected via the existing telecom infrastructure to form a network of phase-stabilized network nodes.

We chose beam clocks of alkaline-earth metal atoms as the platform for our devices. Such clocks, using calcium as the atomic species (linewidth 370 Hz) have been pioneered by the NIST group, and we will follow their footsteps. To test their performance, we will put one of these clocks into an elevator: based purely on the gravitational redshift, we will use the reading of the clock to tell at which floor the elevator is.

The transition wavelength in calcium is at 657 nm, far away from the infra-red wavelength used in telecommunication. We will use wavelength conversion in nonlinear crystals to convert light at infra-red wavelength to the visible wavelength range.

On this project, we cooperate with the Max Planck Institute for Radio Astronomy (MPIfR) to explore the suitability of these clocks for the synchronization of arrays of radio telescopes, as well as with the geodesy people from the University of Bonn. The development of such clocks is perfectly aligned with the current Quantum Flagship initiative of the European Union. 

The OT4Q project: Optical technologies for quantum computation


The ML4Q collaboration is a recently established network between the universities of Aachen, Cologne, and Bonn, as well as the FZ Jülich. The acronym "ML4Q" means Light and Matter for Quantum Communication, so that's what this project is about: the development of concepts and devices for future quantum computing. Within this Cluster of Excellence, we will develop optical technologies required for large-area communication, for example wavelength conversion at the single-photon level, which is required to link platforms operating at different wavelengths.

Also, we investigate the element Zinc as candidate for very robust and compact optical clocks, which might then be used for network synchronization. 



The Pulsars&Clocks project: Linking pulsars and optical clocks



Pulsars are neutron stars in our galaxy that rotate at a very stable frequency, sending out radiowaves that can be detected on Earth as pulses. The arrival time of these pulses is perturbed by various effects, such as processes in the neutron star itself, the orbit of Earth around the sun, and even gravitational waves! Thus, measuring the arrival times of the pulses very precisely allows us to study all these effects. Time-keeping is currently limited by the performance of the maser used for this purpose, and we investigate ways to improve the maser performance through updates from an optical clock.

In addition, we search for ways in which the extreme long-term stability of pulsars (after all, they have been rotating already for many million years) can utilized to improve the long-term stability of optical clocks, which tend to drift away after some time. 





The Gyroscope project: A passive ring laser for geodesy


It is impossible to perform an experiment that measures whether one's inertial frame is moving or not. But the opposite is true for rotations: we can perform experiments (also very precise ones!) to measure rotation rates, e.g. via the Sagnac effect. These ring laser gyroscopes come in two versions: as fiber-optic gyroscopes (very fast and compact, and used in every airplane), and as active ring lasers (very precise, for long-term geodetic and seismic measurements). In this project, we want to forward a third and hitherto poorly explored version: passive ring lasers, where an external laser is locked to a ring cavity. We claim to know a little bit about optical cavities, so we are eager to push the limits of these gyroscopes.

This project is in close collaboration with the geodesy group of Prof. Kusche, and received start-up funding through the Transdisciplinary Research Area (TRA) "Matter". 




Startup funding for these research projects is provided by the University of Bonn, the European Union (ERC Starting Grant 2017), the SFB/TR 185 “OSCAR”, and the Deutsche Forschungsgemeinschaft (DFG) though various programs, among them the Cluster of Excellence ML4Q.

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