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Prof. Dr. Tobias Schätz

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Faculty of Mathematics and Physics
Institute of Physics
Atomic, Molecular and Optical Physics
Hermann-Herder-Straße 3, 79104 Freiburg

Phone: +49(0) 761 / 203-5880
Fax: +49(0) 761 / 203-5881
Email: tobias.schaetz@physik.uni-freiburg.de
Website: http://www.frias.uni-freiburg.de/en/people/fellows/current-fellows/schaetz/#CV

Freiburg Institute for Advanced Studies (FRIAS)



Experimental Atomic, Molecular, and Optical Physics
PAULA - Linear Quantum-Spin Systems,
KINKS - Simulating Discrete Solitons,
BERMUDA - 2D Quantum Systems in Surface-Electrode Traps,
TIAMO - Trapping Ions in Atoms and Molecules Optically

PAULA - Linear Quantum-Spin Systems
Richard Feynman originally proposed to use a well-controlled quantum system to efficiently tackle problems that are too complex to be addressed with classical computers, such as quantum dynamics of many body systems; he called his hypothetical device a quantum computer (QC). Today, we classify it as an analog quantum simulator (AQS) to distinguish it from a QC, in which the dynamics of a system are implemented via algorithms of gate operations on subsets of qubits. In an AQS the strategy is to adiabatically evolve a quantum system from an experimentally well-prepared (initial) state to a new state by changing its Hamiltonian in a controlled manner, to reveal, for example, highly non-trivial dynamics, such as quantum phase transitions. Either device, QC and AQS, may help to develop insights into underlying physics. In addition, well-controlled quantum systems may enable to simulate processes in quantum chemistry and (quantum) biology, such as photosynthesis, where it is under debate whether the laws of quantum mechanics could also influence biological and other macroscopic objects. In any cases, we may gain a deeper understanding of the essential ingredients by directly observing a controlled model quantum system.

KINKS - Simulating Discrete Solitons
In collaboration with Tel-Aviv University we study experimentally and theoretically structural defects, which are formed during the transition from a laser cooled ion cloud to a Coulomb crystal, consisting of tens of ions. We demonstrate the creation of predicted topological defects (`kinks') in purely two-dimensional crystals, and also find kinks which show novel dynamical features in a regime of parameters not considered before. The kinks are always observed at the centre of the trap, showing a large nonlinear localized excitation, and the probability of their occurrence surprisingly saturates at ~0.5. Simulations reveal a strong anharmonicity of the kink's internal mode of vibration, due to the kink's extension into three dimensions. As a consequence, the periodic Peierls-Nabarro potential experienced by a discrete kink becomes a globally confining potential, capable of trapping one cooled defect at the center of the crystal.

BERMUDA - 2D Quantum Systems in Surface-Electrode Traps
Scaling experimental quantum simulations based on ions might allow addressing intriguing quantum effects in many different fields of physics. Three ions residing in three individual traps are suited to simulate anti-ferromagnetic interactions between three quantum spins. This leads to puzzling effects already within this basic triangular configuration. Classically, only two neighboring spins can be orientated in an anti-ferromagnetic manner. The third spin cannot satisfy both neighbors, and hence, "becomes frustrated". Quantum mechanically, a superposition of all frustrated permutations, an entangled state, arises "naturally", leaving the individual spins undetermined while maximizing their correlations. In the envisioned, two-dimensional array of individually trapped ions, the whole quantum ensemble of spins evolves adiabatically, via a quantum-phase-transition into a tremendously complex, entangled state. The frustration in triangular spin lattices, for example, is suspected to be responsible for high Tc superconductivity and may remain unaccessible by classical approaches.

TIAMO - Trapping Ions in Atoms and Molecules Optically Our group had achieved optical trapping of an ion in a dipole trap, recently followed by a 1D-optical lattice. There is a long-term prospect for scaling 2D quantum simulations in optical lattices, based on ions or even on ions and atoms. However, our current project of optically trapping an ion within a BEC of atoms is dedicated to overcome fundamental limitations set by micro-motion when combining optical and rf-trapping. We want to study how chemical reactions proceed at lowest temperatures? The classical concept predicts that approaching zero velocity is equivalent to a standstill of any dynamics. On the one hand, deviations can be expected, since the classical model is ceasing to be appropriate when particle-wave dualism is gaining importance. On the other hand, we might see quantum mechanical properties as minor corrections. However, in the regime of lowest temperatures quantum effects dominate and chemistry is predicted to obey fundamentally different rules. As a consequence, quantum chemistry might permit to control reactions and their pathways by external fields, since forces and related interactions become relevant compared to the kinetic energy. In collaboration with R. Mozynski (Univ. of Warsaw) we aim to study ultra-cold formation of BaRb+ within our optical traps. In a different context, however, developing the basic toolbox for operation, we performed a pump-probe experiment (5fs UV-pulses) on a single molecular ion. In collaboration with R. Cote (Univ. of Connecticut) we elaborate on options how to observe a BEC bound to an ion.

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