# 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

Reserach 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**

D. Schütze, K. Holz, J. Müller, M.K. Beyer, U. Lüning, B. Hartke: Pinpointing Mechanochemical Bond Rupture by Embedding the Mechanophore into a Macrocycle. *Angewandte Chemie Int. Ed.* 54, 2556-2559 (2015); *Angewandte Chemie* 127, 2587-2590 (2015)

I. S. Parry, A. Kartouzian, S. M. Hamilton, O. P. Balaj, M. K. Beyer, S. R. Mackenzie: Chemical Reactivity on Gas-Phase Metal Clusters Driven by Blackbody Infrard Radiation. *Angewandte Chemie Int. Ed.,* 54, 1357-1360 (2015); *Angewandte Chemie*, 127, 1373-1377 (2015)

A. Akhgarnusch, R. F. Höckendorf, Q. Hao, K. P. Jäger, C.-K. Siu, M. K. Beyer: Carboxylation of Methyl Acrylate by Carbon Dioxide Radical Anions in Gas-Phase Water Clusters Angew. Chem. 125, 9497-9500 (2013); Angew. Chem. Int. Ed. 52, 9327-9330 (2013)

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

Institute for Theoretical Physics

Reserach area(s): Quantum computation, information, and control

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

**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**

G. Paparo, V. Dunjko, A. Makmal, M. A. Martin-Delgado, H. J. Briegel: Quantum Speedup for Active Learning Agents. Phys. Rev. X 4, 031002, (2014)

J. Cai, G. G. Guerreschi, H. J. Briegel: Quantum control and entanglement in a chemical compass. Phys. Rev. Lett. 104, 220502 (2010)

H. J. Briegel, D. Browne, W. Dür, R. Raussendorf, M. van den Nest: Measurement-based quantum computation. Nature Physics 5, 19, (2009)

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

Institute for Experimental Physics

Reserach 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**

A. Frisch, M. Mark, K. Aikawa, F. Ferlaino, J. L. Bohn, C. Makrides, A. Petrov, S. Kotochigova: Quantum Chaos in Ultracold Collisions of Erbium Nature 507, 475-479 (2014)

K. Aikawa, A. Frisch, M. Mark, S. Baier, R. Grimm, F. Ferlaino: Reaching Fermi Degeneracy via Universal Dipolar Scattering Phys. Rev. Lett. 112, 010404 (2014)

K. Aikawa, A. Frisch, M. Mark, S. Baier, A. Rietzler, R. Grimm, F. Ferlaino: Bose-Einstein Condensation of Erbium Phys. Rev. Lett. 108, 210401 (2012)

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

Institute for Experimental Physics

Reserach 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)

L. A. Sidorenkov, M. K. Tey, R. Grimm, Y.-H. Hou, L. Pitaevskii, S. Stringari: Second sound and the superfluid fraction in a Fermi gas with resonant interactions. Nature 498, 78 (2013)

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

Reserach area(s): Superconducting quantum circuits

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

**Research interests**

The research in this group is based on superconducting electrical circuits and Josephson junctions, which are used to realize a circuit quantum electrodynamics (cQED) system. The ability to design the level structure of these superconducting circuits, using the non-linearity of the Josephson Junction allows us to engineer artificial atoms and couple them to electrical resonators. These systems are one of the prototypes for studying light-matter interactions on the quantum level akin to more standard cavity QED experiments.

Research has focused on extending the coherence time of these artificial atoms close to 100 μs and further understanding the decoherence mechanisms. Also the ability to design and control these systems has increased tremendously, enabling the implementation of quantum logic gates, proof of principle quantum error correction and the exploration of unstudied quantum optical phenomena.

The goal of my group is to use state of the art qubit and resonator design to realize systems with long coherence times and strong dispersive coupling between the cavity and the qubit. With these systems, we will study ways to implement quantum information protocols and realize quantum optics experiments. A strong focus will lie on the realization of experiments doing quantum simulation of Ising and Heisenberg Models as well as recently proposed implementations of Lattice Gauge Theories. Here we also have to answer the question on how to control and manipulate more and more complex quantum systems. A second line of research will focus on combining cQED systems with other quantum systems to create novel hybrid devices. In such an approach one can benefit from the long coherence time and sophisticated control schemes available for e.g. AMO systems on one side and the fast operations and the readily available electrical interfacing offered by superconducting qubits on the other. Such systems would allow entanglement between optical photons and superconducting qubits, which can be used to build quantum repeaters. Such a hybrid approach also opens up the possibility of combining cQED systems with micromechanical oscillators. Here one could use the microwave circuit to prepare, manipulate and readout the micromechanical oscillator.

**Three selected publications**

L. Sun, A. Petrenko, Z. Leghtas, B. Vlastakis, G. Kirchmair, K. M. Sliwa, A. Narla, M. Hatridge, S. Shankar, J. Blumoff, L. Frunzio, M. Mirrahimi, M. H. Devoret, R. J. Schoelkopf: Tracking photon jumps with repeated quantum non-demolition parity measurement Nature 511, 444 (2014)

B. Vlastakis, G. Kirchmair, Z. Leghtas, S. E. Nigg, L. Frunzio, S. M. Girvin, M. Mirrahimi, M. H. Devoret, R. J. Schoelkopf: Deterministically encoding quantum information in 100-photon Schrödinger cat states Science 342, 607 (2013)

Z. Leghtas, G. Kirchmair, B. Vlastakis, R. J. Schoelkopf, M. H. Devoret, M. Mirrahimi: Hardware-efficient autonomous quantum memory protection Phys. Rev. Lett. 111, 120501 (2013)

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

Institute for Theoretical Physics

Reserach 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.

**Three selected publications**

W. Dür, M. Skotiniotis, F. Fröwis, B. Kraus: Improved quantum metrology using quantum error-correction. Phys. Rev. Lett. 112, 080801 (2014)

J. de Vicente, C. Spee, B. Kraus: Maximally entangled sets of multipartite states. Phys. Rev. Lett. 111, 110502 (2013)

J. I. de Vicente, T. Carle, C. Streitberger, B. Kraus: Complete set of operational measures for the characterization of 3-qubit entanglement: Phys. Rev. Lett. 108, 041805 (2012)

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**Univ.-Prof. Dr. Andreas Läuchli**

Institute for Theoretical Physics

Reserach 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**

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)

Z. Liu, E.J. Bergholtz, H. Fan and A.M. Läuchli: Fractional topological insulators in flat bands with higher Chern number. Phys. Rev. Lett. 109, 186805 (2012)

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

Institut for Experimental Physics

Reserach area(s): Quantum quenches in 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. J. Mark, E. Kirilov, K. Lauber, P. Weinmann, M. Gröbner, A. J. Daley, H.-C. Nägerl; Observation of many-body dynamics in long-range tunneling after a quantum quench. Science 344, 1259 (2014)

F. Meinert, M. J. Mark, E. Kirilov, K. Lauber, P. Weinmann, A. J. Daley, H.-C. Nägerl; Quantum quench in an atomic one-dimensional Ising chain. Phys. Rev. Lett. 111, 053003 (2013)

E. Haller, R. Hart, M.J. Mark, J.G. Danzl, L. Reichsöllner, M. Gustavsson, M. Dalmonte, G. Pupillo, H.-C. Nägerl; Pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons. Nature 466, 597 (2010)

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

Institute for Astro- und Particle Physics

Reserach 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)

M.F. Nieva, N. Przybilla: Present-Day Cosmic Abundances. A comprehensive study of nearby early B-type stars and implications for stellar and Galactic evolution and interstellar dust models. Astron. Astrophys, 539, A143 (2012)

R.P. Kudritzki, M.A. Urbaneja, Z. Gazak, F. Bresolin, N. Przybilla, W. Gieren, G. Pietrzynski: Quantitative Spectroscopy of Blue Supergiant Stars in the Disk of M81: Metallicity, Metallicity Gradient and Distance. Astrophysical Journal, 747, 15 (2012)

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

Institute for Theoretical Physics

Reserach 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**

T. Maier, S. Krämer, L. Ostermann, H. Ritsch: Superradiant clock laser using a magic wavelength optical lattice (2014) Optics Express 22, 13269 (2014)

S. Ostermann, M. Sonnleitner, H. Ritsch: Scattering approach to two-colour light forces and self-ordering of polarizable particles, New Journal of Physics 16, 043017 (2014)

E. Boukobza, H. Ritsch, Breaking the Carnot limit without violating the second law: A thermodynamic analysis of off-resonant quantum light generation, Phys. Rev. A 87, 063845 (2013)

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

Institute for Ion Physics and Applied Physics

Reserach 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, M. Daxner, J. Postler, S.E. Huber, S. Denifl, P. Scheier, and J.P. Toennies, Detection of Negative Charge Carriers in Superfluid Helium Droplets: The Metastable Anions He*– and He_{2}*–. J. Phys. Chem. Lett. 5 2444–2449 (2014)

M. Daxner, S. Denifl, P. Scheier, and A.M. Ellis, Electron-driven self-assembly of salt nanocrystals in liquid helium. Angew. Chem. Int. Ed. 53, 13528–13531 (2014)

A. Mauracher, M. Daxner, S.E. Huber, J. Postler, M. Renzler, S. Denifl, P. Scheier, and A.M. Ellis, Formation of Dianions in Helium Nanodroplets. Angew. Chem. Int. Ed. 53, 13794–13797 (2014) .

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

Institute for Experimental Physics

Reserach 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**

H. Jayakumar, A. Predojević, T. Kauten, T. Huber, G. S. Solomon, and G. Weihs: Time-bin entangled photons from a quantum dot. Nature Commun. 5 (2014)

C. Erven, E. Meyer-Scott, K. Fisher, J. Lavoie, B. L. Higgins, Z. Yan, C. J. Pugh, J. P. Bourgoin, R. Prevedel, L. K. Shalm, L. Richards, N. Gigov, R. Laflamme, G. Weihs, T. Jennewein, and K. J. Resch: Experimental three-photon quantum nonlocality under strict locality conditions. Nature Photonics 8, 292 (2014)

R. Horn, P. Abolghasem, B. J. Bijlani, D. Kang, A. S. Helmy, and G. Weihs: Monolithic Source of Photon Pairs. Phys. Rev. Lett. 108, 153605 (2012)

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

Institute for Ion Physics and Applied Physics

Reserach 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**

J. Mikosch, J. Zhang, S. Trippel, C. Eichhorn, R. Otto, R. Sun, W. DeJong, M. Weidemüller, W. L. Hase, R. Wester: Indirect dynamics in a highly exoergic substitution reaction J. Am. Chem. Soc. 135, 4250 (2013)

R. Otto, J. Brox, S. Trippel, M. Stei, T. Best, R. Wester: Single solvent molecules can affect the dynamics of substitution reactions Nature Chem. 4, 534 (2012)

T. Best, R. Otto, S. Trippel, P. Hlavenka, A. von Zastrow, S. Eisenbach, S. Jezouin, R. Wester, E. Vigren, M. Hamberg, W. D. Geppert: Absolute photodetachment cross-section measurements for hydrocarbon chain anions Astrophys. J. 742, 63 (2011)