# Faculty

The faculty consists of 13 participating researchers from the four physics institutes of the University of Innsbruck.

**Univ.-Prof. Dr. Martin Beyer**

Institute for Ion Physics and Applied Physics

Research area(s): Chemical physics

Keywords: ionic clusters, photochemistry, action spectroscopy, ion cyclotron resonance mass spectrometry, atomic force microscopy, single molecule force spectroscopy

**Research interests**

We investigate chemical reactions in well-defined nanoscale objects. Ionic clusters in the gas phase, e.g. water clusters with an excess electron, or transition metal clusters, serve as model systems for radical anion chemistry or catalysis. Thermochemistry is studied by nanocalorimetry, i.e. by counting the number of solvent molecules evaporating from the cluster. The mass spectrometric methods are combined with optical spectroscopy to obtain a complete characterisation of the studied species. As a second major thrust area, covalently anchored single molecules are studied by atomic force microscopy. The kinetics of mechanochemical reactions is analyzed by applying force-ramp and force-clamp techniques.

**Three selected publications**

Ončák, T. Taxer, E. Barwa, C. van der Linde, M. K. Beyer: Photochemistry and Spectroscopy of Small Hydrated Magnesium Clusters Mg^{+}(H_{2}O)_{n}, n = 1–5. *J. Chem. Phys.* 149, 044309 (2018)

K. Bersenkowitsch, M. Ončák, J. Heller, C. van der Linde, M. K. Beyer: Photodissociation of Sodium Iodide Clusters Doped with Small Hydrocarbons. *Chem. Eur. J.* 24, 12433-12443 (2018).

K. Bersenkowitsch, M. Ončák, C. van der Linde, A. Herburger, M. K. Beyer: Photochemistry of glyoxylate embedded in sodium chloride clusters, a laboratory model for tropospheric sea-salt aerosols. *Phys. Chem. Chem. Phys.* 20, 8143-8151 (2018).

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**Univ.-Prof. Dr. Hans J. Briegel**

Institute for Theoretical Physics

Research area(s): Quantum computation, information, and learning

Keywords: measurement-based quantum computation, cluster states with atoms in optical lattices, quantum many-body entanglement, quantum non-equilibrium systems, quantum machine learning.

**Research interests**

Hans Briegel’s research topics include fundamental notions of quantum mechanics, such as measurement, entanglement, and de‐coherence, their experimental signatures and their implications for our understanding of complex many-body systems. One of his main current interests is to understand the ultimate power of machines to compute and to simulate Nature. Models for quantum information processing, both in physical and in biological systems, are thereby being explored.

**Three selected publications**

V. Dunjko, H. J. Briegel: Machine learning & artificial intelligence in the quantum domain Rep. Prog. Phys. 81, 074001 (2018)

H. Poulsen Nautrup, N. Friis, and H. J. Briegel: Fault-tolerant interface between quantum memories and quantum processors Nat. Commun. 8, 1321 (2017)

V. Dunjko, J. M. Taylor, H. J. Briegel: Quantum-Enhanced Machine Learning Phys. Rev. Lett. 117, 130501 (2016)

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**Univ.-Prof. Dr. Francesca Ferlaino - Deputy Speaker of the Doctoral Programme**

Institute for Experimental Physics

Research area(s): Condensed matter physics with atomic dipolar gases

Keywords: Ultracold atoms, dipolar quantum gases, Bose-Einstein condensation, degenerate Fermi gases, laser cooling, atom-light interaction, Feshbach resonances, ultracold molecules, polar molecules, tunable gases, quantum many-body physics, quantum magnetism, spin-orbit coupled quantum systems, Efimov states, few-body physics

**Research interests**

The central research interest of the Faculty Member is the study and understanding of quantum systems in presence of strong dipolar interaction. Our interest focuses on both quantum few- and the many-body aspects of ultracold dipoles. As system, we use a highly magnetic atomic species, erbium (Er), which belongs to the family of lanthanides. The use of this unconventional – and rather unexplored – atomic species has also naturally enlarged our interest beyond dipolar physics. Erbium as sub-merged shell atom has an exotic electronic structure, characterized by a highly anisotropic charge distribution in the electronic ground state. All this makes Er a novel case for scattering and many-body physics with phenomena that drastically differ from usual closed-shell atoms, such as alkali and open novel fascinating research frontiers.

**Three selected publications**

Trautmann, P. Ilzhöfer, G. Durastante, C. Politi, M. Sohmen, M. J. Mark, F. Ferlaino: Dipolar Quantum Mixtures of Erbium and Dysprosium Atoms Phys. Rev. Lett. 121, 213601 (2018)

L. Chomaz, R. M. W. van Bijnen, D. Petter, G. Faraoni, S. Baier, J. H. Becher, M. J. Mark, F. Waechtler, L. Santos, F. Ferlaino: Observation of roton mode population in a dipolar quantum gas Nature Physics 14, 442-446 (2018)

S. Baier, M. J. Mark, D. Petter, K. Aikawa, L. Chomaz, Z. Cai, M. Baranov, P. Zoller, F. Ferlaino: Extended Bose-Hubbard models with ultracold magnetic atoms Science 352, 201-205 (2016)

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**Univ.-Prof. Dr. Rudolf Grimm**

Institute for Experimental Physics

Research area(s): Strongly interacting quantum gases

Keywords: Ultracold atoms, ultracold molecules, tunable quantum gases, Bose-Einstein condensation, degenerate Fermi gases, quantum gas mixtures, Feshbach resonances, quantum many-body physics, quantum simulations, strongly interacting quantum systems, fermionic superfluidity, Efimov states, few-body physics

**Research interests**

The general research interest of the faculty member is the complex physics of matter under conditions of strong interactions governed by the rules of quantum mechanics. The basic experimental approach is to create and investigate model systems composed of ultracold atomic and molecular gases at temperatures in the nanokelvin range, which offer a superb level of control and accessibility. The basic building blocks are laser-coolable atoms of various species (alkali, earth-alkaline, lanthanoid) and different quantum statistics (bosons and fermions). An essential tool are external optical potentials created by far detuned laser light, which allow to realize different confinement situations, such as low-dimensional structures or optical lattices. Another important tool is the interaction control via so-called Feshbach resonances. These ingredients give a large variety of possibilities to realize few- and many-body quantum systems and to study their microscopic and macroscopic properties.

A particular research interest of the faculty member consists in ultracold fermionic systems, which are of great fundamental relevance as all basic building blocks of matter belong to the class of fermions (electrons, protons, neutrons, or also quarks). Fermionic quantum gases allow the simulation of various interesting states related to fundamental phenomena in condensed-matter physics. For example, superfluid states, paired states, and polaronic states have been investigated by the group of the faculty member. Because of recent experimental progress in the preparation of ultracold systems, new systems have become available or will become available soon, which considerably widen the experimental possibilities. Mass-imbalanced fermionic systems are one of the new frontiers of the field, which is a main focus of research of the group.

Another particular research interest is the physics of few-body systems, which represents a research field on its own right, lying between elementary two-body physics and many-body physics and exhibiting specific phenomena. Few-body interactions can have profound consequences on the many-body physics of a strongly interacting quantum matter. A new frontier in the field is represented by systems with mass imbalance, which show intriguing new effects that have no counterpart in mass-balanced systems.

**Three selected publications**

B. Huang, L. A. Sidorenkov, R. Grimm, J. M. Hutson: Observation of the second triatomic resonance in Efimov’s scenario. Phys. Rev. Lett. 112, 190401 (2014)

M. Cetina, M. Jag, R. S. Lous, I. Fritsche, J. T. M. Walraven, R. Grimm, J. Levinsen, M. M. Parish, R. Schmidt, M. Knap, E. Demler: Ultrafast many-body interferometry of impurities coupled to a Fermi sea. Science 354, 96 (2016)

C. Kohstall, M. Zaccanti, M. Jag, A. Trenkwalder, P. Massignan, G. M. Bruun, F. Schreck, and R. Grimm: Metastability and coherence of repulsive polarons in a strongly interacting Fermi mixture. Nature 485, 615 (2012)

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**Univ.-Prof. Dr. Gerhard Kirchmair**

Institute for Experimental Physics

Research area(s): Superconducting quantum circuits

Keywords: Superconducting qubits, quantum circuits, circuit QED, quantum information, quantum optics, quantum repeaters, quantum simulation

**Research interests**

Our research is based on superconducting electrical circuits and Josephson junctions, which are used to realize a circuit quantum electrodynamics (cQED) system. These circuits are built out of superconducting metallic structures fabricated by electron beam lithography and are operated inside a dilution refrigerator at 10 mK. The ability to design the level structure of these artificial atoms by changing the layout of the samples allows us to engineer their properties and couple them to electrical resonators. The research of the group is divided in different projects:

The aim of the first project is to experimentally implement a platform for analog quantum simulation of interacting spin models arranged in one and two-dimensional geometries. The scheme capitalizes on the remarkable recent developments in circuit Quantum Electro Dynamics (cQED), especially the 3D transmon qubit. The central idea behind this work is to exploit naturally occurring dipolar interactions between two superconducting 3D transmon qubits to engineer the desired spin-spin interactions. For the two qubit interaction we choose to use the pairwise spin-spin coupling where the strength depends on the distance and respective angles of the qubits. This interaction is three to four orders of magnitude larger than the decoherence rates for typical 3D transmon qubits and will dominate the properties of the system. Combining this interaction with the ability to arrange the qubits on essentially arbitrary geometries paves the way to the realization of a broad class of dipolar spin models ranging from linear spin chains to ladder geometries (see Fig. 1). Together with Peter Zoller and his group, we have developed a scheme that promises a faithful implementation of many-body spin-1/2 Hamiltonians involving tens of qubits (Muppalla et al. 2018). Currently we are implementing and investigating the tools and methods required for building such a system.

In the second project our goal is to set up a new type of experiment in which the coupling between mechanics and circuits is achieved inductively. This architecture is suited for detecting and cooling the motion of a mechanical oscillator (i.e. cantilever) to the quantum ground state and achieve strong coupling. Ultimately, we aim at reaching the single-photon single-phonon strong coupling regime, where the exchange between a single photon and a single phonon can be achieved deterministically. Such a regime would allow for the full quantum control of a macroscopic mechanical object, opening numerous opportunities for technological applications as well as fundamental studies. In a first step towards this goal, we want to detect the motion of the cantilever via magnetic readout using a superconducting quantum interference device (SQUID). We have recently achieved this goal and are working on improving the system parameters to reach the strong resolved sideband regime

**Three selected publications**

P.R. Muppalla, O. Gargiulo, B. P. Venkatesh, L. Gruenhaupt, I. Pop, G. Kirchmair: Bi-stability in a Mesoscopic Josephson Junction Array Resonator** **Phys. Rev.* B* 97, 024518 (2018)

M. Dalmonte, S. Mirzaei, P. R. Muppalla, D. Marcos, P. Zoller, G. Kirchmair: Dipolar Spin Models with Arrays of Superconducting Qubits Phys. Rev. B 92, 174507 (2015)

G. Via, G. Kirchmair, O. Romero-Isart: Strong Single-Photon Coupling in Superconducting Quantum Magnetomechanics Phys. Rev. Lett. 114, 143602 (2015)

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**Assoc. Prof. Dr. Barbara Kraus**

Institute for Theoretical Physics

Research area(s): Quantum many-body systems

Keywords: Quantum Information Theory, multipartite entanglement, experimental realization of quantum information processing tasks, quantum computation, Kolmogorov complexity

more details »

**Research interests**

Our main research interests are fundamental problems within Quantum Information Theory. We focus on the development of novel theoretical tools for the investigation of quantum many-body systems. One of the aims is the characterization of the entanglement and complexity properties of multipartite systems. More precisely, we address the problem of many-body quantum systems with the main aim to discover new applications of multipartite states; the identification of the properties which make them useful for those applications; proposals of new methods for the experimental realization of quantum information processors. Moreover, we develop novel tools for the generation and manipulation of multipartite entangled states in specific experimental set-ups, like trapped ions or atoms in optical lattices. Furthermore, we are working on compressed quantum computation and on various methods to verify quantum information processors.

**Three selected publications**

M. Hebenstreit, B. Kraus, L. Ostermann, H. Ritsch, *Subradiance and entanglement in atoms with several independent decay channels,* Phys. Rev. Lett. **118**, 143602 (2017)

C. Spee, J.I. de Vicente, D. Sauerwein, B. Kraus, *Entangled Pure State Transformations via Local Operations Assisted by Finitely Many Rounds of Classical Communication*, Phys. Rev. Lett. **118**, 040503 (2017)

D. Sauerwein, N. R. Wallach, G. Gour, B. Kraus, *Transformations among pure multipartite entangled states via local operations are almost never possible*, Phys. Rev. X **8**, 031020 (2018)

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**Univ.-Prof. Dr. Andreas Läuchli**

Institute for Theoretical Physics

Research area(s): Non-equilibrium dynamics of cold atoms and interacting light

Keywords: Quantum many-body systems, ultracold quantum gases, non-equilibrium dynamics, matter-light interaction

**Research interests**

The research of Andreas Läuchli is devoted to the theoretical study of strongly interacting quantum many body systems arising in condensed matter systems and ultracold quantum gases. Large-scale computer simulations allow to uncover and to understand phenomena that are often difficult to tackle based on analytical methods alone. Fields of current interests are exotic quantum states of matter in e.g. quantum magnets or ultracold multispecies fermions, nonequilibrium dynamics of correlated quantum systems, and the development and application of quantum information inspired tools enabling a deeper understanding of quantum many body systems.

**Three selected publications**

M. Rader, A.M. Läuchli: Finite Correlation Length Scaling in Lorentz-Invariant Gapless iPEPS Wave Functions. Phys. Rev. X 8, 031030 (2018)

N.Y. Yao, A.V. Gorshkov, C.R. Laumann, A.M. Läuchli, J. Ye, and M.D. Lukin: Realizing Fractional Chern Insulators with Dipolar Spins. Phys. Rev. Lett. 110, 185302 (2013)

P. Corboz, M. Lajko, A.M. Läuchli, K. Penc, and F. Mila: Spin-orbital quantum liquid on the honeycomb lattice. Phys. Rev. X 2, 041013 (2012)

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**Univ.-Prof. Dr. Hanns-Christoph Nägerl**

Institut for Experimental Physics

Research area(s): Dynamics of quantum many-body systems

Keywords: Ultracold quantum matter, quantum many-body physics, Bose-Einstein condensation, low-dimensional quantum systems, ultracold molecules, matter-wave interferometry, quantum simulation, dipolar quantum gases, long-range interactions, quantum phase transitions, quantum magnetism, quantum quenches and quantum non-equilibrium physics.

**Research interests**

The interests of Hanns-Christoph Nägerl lie in the generation and control of quantum many-body systems. The goal is to perform experimental quantum simulations that outperform classical computations. By this, the group wants to study new forms of quantum matter, new quantum phenomena, and novel dynamical systems. To this end they study ground-state properties (quantum phases, quantum phase transitions,…) and dynamical many-body quantum processes (quantum quenches, non-equilibrium quantum many-body systems, thermalization).

**Three selected publications**

F. Meinert, M. Knap, E. Kirilov, K. Lauber, M. B. Zvonarev, E. Demler, and H.-C. Nägerl: Bloch oscillations in the absence of a lattice. Science 356, 945 (2017)

L. Reichsöllner, A. Schindewolf, T. Takekoshi, R. Grimm, and H.-C. Nägerl: Quantum engineering of a low-entropy gas of heteronuclear bosonic molecules in an optical lattice. Phys. Rev. Lett. 118, 073201 (2017)

E. Haller, M. Gustavsson, M.J. Mark, J.G. Danzl, R. Hart, G. Pupillo, H.-C. Nägerl, Realization of an Excited, Strongly Correlated Quantum Gas Phase. Science 325, 1224 (2009)

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**Univ.-Prof. Dr. Norbert Przybilla**

Institute for Astro- und Particle Physics

Research area(s): Quantitative spectroscopy in astrophysics

Keywords: radiative transfer, atomic & molecular physics, quantitative spectroscopy, stellar atmospheres, stellar evolution

**Research interests**

The group of Norbert Przybilla is interested in observation, modelling and analysis of astrophysical plasmas, by means of quantitative spectroscopy, and in particular of stellar atmospheres in order to determine their physical parameters and abundances of chemical elements. The accuracy & precision of analyses can be improved with novel approaches to the modelling of the interaction of light with matter (atoms/ molecules/ions) in astrophysical plasmas. By using precise observational constraints they aim to understand stellar evolution, the interstellar medium and the formation and evolution of galaxies.

**Three selected publications**

A.F. Marino, A.P. Milone, N. Przybilla, M. Bergemann, K. Lind, M. Asplund, S. Cassisi, M. Catelan, L. Casagrande, A. Valcarce, L.R. Bedin, C. Cortés, F. D’Antona, H. Jerjen, G. Piotto, M. Zoccali, R. Angeloni: Helium enhanced stars in the globular cluster NGC2808: spectroscopic measurements on blue horizontal branch stars. Monthly Notices of the Royal Astronomical Society, 437, 1609 (2014)

A. Maeder, N. Przybilla, M.F. Nieva, C. Georgy, G. Meynet, S. Ekström, P. Eggenberger: Evolution of surface CNO abundances in massive stars. Astron. Astrophys., 565, A39 (2014)

N. Przybilla, L. Fossati, S. Hubrig, M.F. Nieva, S.P. Järvinen, N. Castro, M. Schöller, I. Ilyin, K. Butler, F.R.N. Schneider, L.M. Oskinova, T. Morel, N. Langer, A. de Koter, and the BOB collaboration: B fields in OB stars (BOB): Detection of a magnetic field in the He-strong star CPD -57° 3509. Astron. Astrophys., 587, A7 (2016)

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**Univ.-Prof. Dr. Helmut Ritsch**

Institute for Theoretical Physics

Research area(s): Quantum optics and cavity quantum electrodynamics

Keywords: quantum optics, cavity QED, light forces, ultracold gases, laser theory

**Research interests**

Helmut's Ritsch research is focused on cavity QED with cold quantum particles ranging from degenerate quantum gases of atoms and molecules, spin ensembles in cooled solids to nanoparticles coupled high Q resonator fields. In this strongly correlated nonlinear particle-field dynamics the field controlls the particles internal and external dynamics in a well designable way, while at the same time the particles significantly change the field evolution.

This opens the door for studying fundamental questions of quantum physics at the borderline between quantum optics, quantum information science and condensed matter physics. In particular questions of quantum limits of measurements and the properties of mesosscopic quantum superpostions can be studied in such configurations. Ultracold particles moving in the optical lattice potential of a quantized field undergo a quantum phase transition from a homogenoeus superfluid to an ordered crystal with supersolid properties. The cavity mediated long range interactions allow to create long range correlations as well as collective excitations and entanglement in optical lattices and has great potential for new cooling schemes for molecules and nanoparticles towards the quantum regime.

With his team at the Theoretical Physics institute, Professor Ritsch is currently extending the theoretical models to more realistically describe these systems. In parallel his team develops highly memory and time efficient object oriented numerical codes to extend time dependent quantum simulations to larger system sizes.

**Three selected publications**

F. Mivehvar, H. Ritsch, F. Piazza: Cavity-Quantum-Electrodynamical Toolbox for Quantum Magnetism, Phys. Rev. Lett. **122**, 113603 (2019)

S. Krämer, D. Plankensteiner, L. Ostermann, H. Ritsch: QuantumOptics.jl: A Julia framework for simulating open quantum systems, Comp.Phys.Comm 227, 109 (2018)

F. Mivehvar, S. Ostermann, F. Piazza, H. Ritsch: Driven-Dissipative Supersolid in a Ring Cavity, Phys. Rev. Lett. **120**, 123601 (2018)

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**Univ.-Prof. Dr. Paul Scheier**

Institute for Ion Physics and Applied Physics

Research area(s): Nano-bio physics

Keywords: doped He nano droplets, astrochemistry, ion molecule reactions, diffuse interstellar bands

**Research interests**

Clusters and nanoparticles are the focus of the research of Paul Scheier. These systems form a link between the gas phase and the condensed phases and provide a unique possibility to probe phase transitions as well as to build advanced materials with tailor made properties. Cluster formation via pickup of dopants into helium nanodroplets leads to structures similar to molecular films that grow on dust particles in the interstellar medium. Subsequent intra-cluster reactions triggered by electron or photon bombardment provide an unrivaled method to probe molecular synthesis in deep space. Fundamental problems in cluster physics as well as chemical processes at sub-Kelvin temperatures are key research themes of the group “Nano-Bio-Physics”.

**Three selected publications**

A. Mauracher, O. Echt, A.M. Ellis, S. Yang, D.K. Bohme, J. Postler, A. Kaiser, S. Denifl, and P. Scheier, Cold Physics and Chemistry: Collisions, Ionization and Reactions inside Helium Nanodroplets Close to Zero K. *Phys. Rep.* *751* (2018) 1–90

M. Goulart, M. Kuhn, P. Martini, L. Chen, F. Hagelberg, A. Kaiser, P. Scheier, and A.M. Ellis, Highly Stable C_{60}AuC_{60}^{+/-} Dumbbells. *Phys. Chem. Lett.* **9** (2018) 2703–2706

M. Renzler, M. Kuhn, A. Mauracher, A. Lindinger, P. Scheier, and A.M. Ellis, Anionic Hydrogen Cluster Ions as a New Form of Condensed Hydrogen. *Phys. Rev. Lett.* **117** (2016) 273001

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**Univ.-Prof. Dr. Gregor Weihs**

Institute for Experimental Physics

Research area(s): Semiconductor quantum optics

Keywords: semiconductor, quantum dot, exciton-polariton, microcavity, single-photon source, entangled photon pairs

**Research interests**

In his research Gregor Weihs develops integrated quantum nano-photonics. He currently focuses on the physics and applications of quantum mechanical entanglement and experiments on the foundations of quantum mechanics. For future quantum communication technologies one will need efficient, bright, and miniaturized sources of entangled photon pairs as well as other integrated optical elements. Currently his group is working on a variety of sources of non-classical states of light based on semiconductor nanostructures utilizing semiconductor optical waveguides, single quantum dots and strongly coupled semiconductor microcavities. The long term goal is the quantum optical lab-on-a-chip.

**Three selected publications**

M. Prilmüller, T. Huber, M. Müller, P. Michler, G. Weihs, and A. Predojević, *Hyperentanglement of Photons Emitted by a Quantum Dot,* Phys. Rev. Lett. **121**, 110503 (2018)

C. Dittel, G. Dufour, M. Walschaers, G. Weihs, A. Buchleitner, and R. Keil, *Totally Destructive Many-Particle Interference,* Phys. Rev. Lett. **120**, 240404 (2018)

M. Khoshnegar, T. Huber, A. Predojević, D. Dalacu, M. Prilmüller, J. Lapointe, X. Wu, P. Tamarat, B. Lounis, P. Poole, G. Weihs, and H. Majedi, *A solid state source of photon triplets based on quantum dot molecules,* Nat. Commun. **8**, 15716 (2017)

**Univ.-Prof. Dr. Roland Wester - Speaker of the Doctoral Programme**

Institute for Ion Physics and Applied Physics

Research area(s): Spectroscopy and dynamics of molecular systems

Keywords: cold molecular ions, rovibrational and electronic spectroscopy, reaction dynamics, inelastic collisions, astrochemistry

**Research interests**

The research goals of my group are to observe and understand the interactions between molecules on an atomic level. For this purpose we study on the one hand reactive collisions between molecules and ions with well-controlled momentum vectors and internal excitation. On the other hand we employ cryogenic ion traps to study ionic reactions at low temperature and photodetachment of negative ions. Furthermore we are developing methods to control the internal quantum states of the molecules and ions using infrared and far-infrared terahertz radiation. Our work has been successfully providing insight into the detailed dynamics of chemical reactions. Our studies have also provided important quantitative measurements of loss processes of molecular ions that have been found in interstellar molecular clouds and circumstellar envelopes.

**Three selected publications**

S. Spieler, D. F. Dinu, P. Jusko, B. Bastian, M. Simpson, M. Podewitz, K. R. Liedl, S. Schlemmer, S. Brünken, R. Wester: Low frequency vibrational anharmonicity and nuclear spin effects of Cl^{-}(H_{2}) and Cl^{-}(D_{2}) J. Chem. Phys. 149, 174310 (2018)

M. Stei, E. Carrascosa, A. Doerfler, J. Meyer, B. Olasz, G. Czakó, A., Li, H. Guo, R. Wester: Stretching vibration is spectator in nucleophilic substitution Sci. Adv. 4:eaas954 (2018)

O. Lakhmanskaya, M. Simpson, S. Murauer, M. Nötzold, E. Endres, V., Kokoouline, R. Wester: Rotational Spectroscopy of a Triatomic Molecular Anion Phys. Rev. Lett. 120, 253003 (2018)