The coherent control of charged particles such as electrons and ions in free space is currently gaining relevance in fundamental research as well as for technical applications. The focus in my Emmy Noether group "Quantum Electron- & Ion-Interferometry" at the Institute of Physics at the University of Tübingen is on matter wave experiments for charged particles and its applications in sensor technologies.
Experiments with matter waves: interferometry with electrons and ions
In this project, we seek to establish and enhance an electron and ion interferometer based on a device created by Maier and Hasselbach . It opens up novel quantum experiments combining charged matter waves and the inner structure of ions in comparison to the pointlike electrons. The main component in the setup is a novel single-atom tip ion source for intensive, coherent helium and hydrogen ion beams . A nanoscale biprism beam splitter will create a spatial superposition state of the coherent ions and their matter wave will be measured by interference. The device is currently tested with electrons. In strong collaboration with our partners from industry and other universities we thereby developed a highly sensitive method to measure external electromagnetic and vibrational frequencies. The technique is based on the perturbation of the quantum matter wave interference pattern of electrons by such oscillations in combination with second order correlation analysis of the spatial and temporal data in the detector.
Experiments concerning quantum decoherence through Coulomb-interaction
Interesting questions arise in connection with decoherence, being the loss of quantum nature in a system due to the interaction with the environment. The decoherence through Coulomb-interaction is a fascinating field in experimental quantum physics with important applications in quantum logic, surface analysis, microscopy and the realization of hybrid quantum systems.
In this context, one project in our research group studies the decoherence of an electronic and macroscopic superposition
state near semiconducting, metallic or superconducting surfaces. The quantum-classical transition region is analyzed experimentally in a biprism electron interferometer that is based on the
setup of Sonnentag et al. . Thereby our experiment measures the interaction between coherent electrons and normal or superconducting environments. At Berkeley Lab we study the application of this method for novel non-invasive surface probing techniques in electron microscopy.
Development of novel coherent electron field emission sources
In various fields of science and technology, electron beam emitters are applied, such as in electron microscopy, surface spectroscopy, matter wave interferometry or sensor technology. The point of beam origin thereby is in most cases an etched metal nanotip set on a high voltage. In this project, we study the coherent electron emission from superconducting niobium tips with extremely small energy spread. We also test single atom tip field emission in strong collaboration with a cooperation partner in Taiwan. Being a Visiting Scholar at Stanford University, USA, for several months, I also got the opportunity to study and develop ultrashort laser pulsed electron field emission sources. At Berkeley Lab a new project was funded to develop new superconducting coherent electron emitters for electron microscopy and quantum information science applications.
 F. Hasselbach, U. Maier, in: Quantum Coherence and Decoherence: Proc.
ISQM-Tokyo '98, ed. by Y.A. Ono, K. Fujikawa (Elsevier, Amsterdam, 1999), p. 299
 H.S. Kuo, I.S. Hwang, T.Y. Fu et al., Japanese J. Appl. Phys. 45, 8972 (2006)
 P. Sonnentag and F. Hasselbach Phys. Rev. Lett. 98, 200402 (2007)