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. The mass spectrometric methods are combined with optical spectroscopy to obtain a complete characterisation of the studied species. Special focus lies on carbon dioxide activation, hydrogen evolution and ions in the atmosphere. 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

E. Barwa, T. F. Pascher, M. Ončák, C. van der Linde, M. K. Beyer: Carbon Dioxide Activation at Metal Centers: Evolution of Charge Transfer from Mg⁺to CO₂in [MgCO₂(H₂O)_n]⁺, n = 0–8. Angew. Chem. Int. Ed. 59, 7467-7471 (2020); Angew. Chem. 132, 7537-7541 (2020).

A. Herburger, E. Barwa, M. Ončák, J. Heller, C. van der Linde, D. M. Neumark, M. K. Beyer: Probing the Structural Evolution of the Hydrated Electron in Water Cluster Anions (H₂O)_n^–, n≤ 200, by Electronic Absorption Spectroscopy. J. Am. Chem. Soc.141, 18000-18003 (2019).

M.F. Pill, A. L. L. East, D. Marx, M. K. Beyer, H. Clausen-Schaumann: Mechanical activation drastically accelerates amide bond hydrolysis, matching enzyme activity. Angew. Chem. Int. Ed.58, 9787-9790 (2019); Angew. Chem.131, 9890-9894 (2019).

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Research interests

The research interests of Hans Briegel include models for quantum information processing and learning, and fundamental aspects of quantum information. One focus of his research is the theory of measurement-based quantum computation, which has resulted in a new and more thorough understanding of many-body entanglement as resource, and applications in quantum communication, quantum error correction, and quantum algorithms. Another focus lies in quantum machine learning and the development of artificial intelligence and machine learning in basic science. Some of this work is highly interdisciplinary and addresses questions in different fields, including quantum physics, robotics, and the philosophy of action.

Three selected publications

J. Wallnöfer, A. A. Melnikov, W. Dür, H. J. Briegel: Machine learning for long-distance quantum communication, PRX Quantum 1, 010301 (2020)

H. Poulsen Nautrup, N. Delfosse, V. Dunjko, H. J. Briegel, N. Friis: Optimizing quantum error correction codes with reinforcement learning, Quantum 3, 215 (2019)

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

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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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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 and different quantum statistics (bosons and fermions). An essential tool are external optical potentials created by far-detuned laser light, which allow experimentalists to realize different confinement situations, such as low-dimensional structures or optical lattices. Another important tool is the interaction control via 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 special research interest of the faculty member consists in ultracold fermionic systems, which are of great fundamental relevance since 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 research group. 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 represents a main focus of research of the group.

Three selected publications

C. Ravensbergen, E. Soave, V. Corre, M. Kreyer, B. Huang, E. Kirilov, R. Grimm: Resonantly Interacting Fermi-Fermi Mixture of ¹⁶¹Dy and ⁴⁰K, Phys. Rev. Lett. 124, 203402 (2020) 

R. S. Lous, I. Fritsche, M. Jag, F. Lehmann, E. Kirilov, B. Huang, R. Grimm: Probing the Interface of a Phase-Separated State in a Repulsive Bose-Fermi Mixture, Phys. Rev. Lett. 120, 243403 (2018) 

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) 

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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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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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Research interests

Research in my group is devoted to exploring quantum-mechanical interfaces between light and matter and to investigating applications of these interfaces, including quantum networks, quantum sensors, and quantum simulation. For this purpose, we use (a) optical cavities, (b) the electronic and motional degrees of freedom of trapped atomic ions under ultra-high vacuum, and (c) the center-of- mass motion of silica nanoparticles. We have developed methods to transfer quantum information between ions and single photons in optical cavities, and we are currently studying the extension of these methods to multi-node trapped-ion networks over long distances. Our research also focuses on the preparation and characterization of quantum-mechanical states of levitated objects, in particular of nanoscale objects, which offer future perspectives as precision sensors and quantum transducers.

Three selected publications

L. Dania, D. S. Bykov, M. Knoll, P. Mestres, T. E. Northup: Optical and electrical feedback cooling of a silica nanoparticle in a Paul trap, Phys. Rev. Research 3, 013018 (2021)

M. Lee, K. Friebe, D. Fioretto, K. Schüppert, F. R. Ong, D. Plankensteiner, V. Torggler, H. Ritsch, R. Blatt, T. E. Northup: Ion-based quantum sensor for optical cavity photon numbers, Phys. Rev. Lett. 122, 153603 (2019)

B. Casabone, K. Friebe, B. Brandstätter, K. Schüppert, R. Blatt, T. E. Northup: Enhanced quantum interface with collective ion-cavity coupling, Phys. Rev. Lett. 114, 023602 (2015)

 

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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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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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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 C₆₀AuC₆₀^+/- 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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Research interests

 The Photonics group develops integrated quantum photonic circuits for tests of the foundations of quantum mechanics and for applications in quantum information. The waveguide circuits are implemented in semiconductor platforms so that they can include active elements. In particular the group is working on efficient, bright, and miniaturized sources of entangled photon pairs and other non-classical states of light mostly based on single semiconductor quantum dots.  These states are then employed in quantum interferometry experiments.

Three selected publications

J. Münzberg, C. Dittel, M. Lebugle, A. Buchleitner, A. Szameit, G. Weihs, and R. Keil, Symmetry Allows for Distinguishability in Totally Destructive Many-Particle Interference, PRX Quantum 2, 020326 (2021)

H. Chen, S. Auchter, M. Prilmüller, A. Schlager, T. Kauten, K. Laiho, B. Pressl, H. Suchomel, M. Kamp, S. Höfling, C. Schneider, and G. Weihs, Time-bin entangled photon pairs from Bragg-reflection waveguides, APL Photonics 3, 080804 (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)

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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

M. Simpson, M. Nötzold, A. Schmidt-May, T. Michaelsen, B. Bastian, J. Meyer, R. Wild, F. A. Gianturco, M. Milovanovic, V. Kokoouline, R. Wester: Threshold Photodetachment Spectroscopy of the Astrochemical Anion CN- J. Chem. Phys. 153, 184309 (2020)

J. Meyer, E. Carrascosa, T. Michaelsen, B. Bastian, A. Li, H. Guo, R. Wester: Unexpected indirect dynamics in base-induced elimination J. Am. Chem. Soc. 141, 20300 (2019)

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)

Personal webpage /  

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. Another main research interst is the verification of quantum devices. We develop various methods to characterize, verify, and validate quantum processors.

Three selected publications

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)

M. Hebenstreit, R. Jozsa, B. Kraus, S. Strelchuk, M. Yoganathan, All pure fermionic non-Gaussian states are magic states for matchgate computations, Phys. Rev. Lett. 123, 080503 (2019)

J. Carrasco, A. Elben, C. Kokail, B. Kraus, P. Zoller, Theoretical and Experimental Perspectives of Quantum Verification, PRX Quantum 2, 010102

 

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)