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Research Training Group 1729/Leibniz Universität Hannover
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Research Training Group 1729/Leibniz Universität Hannover
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Colloquium 11.04.2012; 10:15; Room D 326

Jun.- Prof. Dr. Roman Ciurylo
Nicolaus Copernicus University

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Optical Feshbach resonances in ultra-cold ytterbium

The results of theoretical studies on photoassociation near the intercombination transition 1S0-3P1 in ultra-cold bosonic ytterbium are presented and compared with experiment. The relation and differences between the photoassociation spectra obtained in homo- and hetero-nuclear case is discussed. The mass scaling of the molecular structure was tested for the excited states.
The applicability of the model to forbidden gerade-gerade transition was also investigated. Finally, the limitation of using simple model potentials in the data analysis of ultra precise photoassociation spectra is discussed.



Colloquium; 12.04.2013; 11:00 h; Room D326

Dr. David Adu Smith
Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin

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Prethermalization in a Non-Equilibrium Many-Body Quantum System

Non-equilibrium many-body quantum systems are not very well understood, particularly with regard to how these systems reach thermal equilibrium. Through the use of one-dimensional ultracold quantum gases, it is possible to monitor the evolution of such a non-equilibrium system and observe the many-body phenomenon prethermalization. In a prethermalized state, certain observables can appear thermal, i.e. in equilibrium, when the system has not in fact reached thermal equilibrium. Such a state has ramifications for fields as diverse as high-energy physics, cosmology and condensed matter, not to mention the production of any future quantum technology that requires the use of non-equilibrium many-body systems.



Colloquium 18.04.2012; 14:00 h; Room D 326

Prof. Dr. Gerhard Rempe
Max Planck Institute of Quantum Optics, Garching

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Molecules Go Cold

Cold dipolar molecules offer new perspectives for the exploration of fundamental physics and the implementation of novel ideas. Towards these goals, generally applicable and sufficiently simple trapping and cooling techniques need to be developed. The talk will discuss some recent experiments in this direction, including the Sisyphus cooling of an ensemble of polyatomic molecules and the centrifuge deceleration of electrically guided molecules on a spinning disk.




Colloquium 25.04.2013; 10:15 h; Room D 326

Prof. Dr. Michael Köhl
University of Cambridge
Department of Physics

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Two-dimensional Fermi gases

Pairing of fermions is ubiquitous in nature and it is responsible for a large variety of fascinating phenomena like superconductivity, superfluidity of 3He, the anomalous rotation of neutron stars, and the BEC-BCS crossover in strongly interacting Fermi gases. When confined to two dimensions, interacting many-body systems bear even more subtle effects, many of which lack understanding at a fundamental level. In particular, the questions how many-body pairing is established at high temperature and whether it precedes superconductivity are crucial to be answered. We report on the observation of pairing in trapped two-dimensional atomic Fermi gas in the regime of strong coupling. We perform momentum-resolved photoemission spectroscopy to measure the spectral function of the gas and we detect pairing gap above the superfluid transition temperature. Moreover, using the same technique, we investigate spin-imbalanced Fermi gases and find evidence for the formation of polarons and their crossover to a dimer state in two dimensions. Finallt, we report on recent experiments on spin-transport in two-dimensional Fermi gases establishing a quantum-mechanical bound for spin diffusion.



Colloquium 21.05.2013; 14:15 h; Room D 326

Prof. Dr. Géza Tóth
University of the Basque Country UPV/EHU
Bilbao, Spain

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Spin squeezing inequalities for entanglement detection in cold gases

We determine the complete set of generalized spin squeezing inequalities, given in terms of the collective angular momentum components, for particles with an arbitrary spin. They can be used for the experimental detection of entanglement in an ensemble in which the particles cannot be individually addressed. We also present a complete set of criteria involving collective observables different from the angular momentum coordinates. We also discuss how our inequalities distinguish between inter-particle and intra-particle squeezing, which is needed for entanglement conditions for particles with a spin larger than 1/2. Our findings are especially useful in the light of recent experiments with spinor condensates and spin nematics.

[1] G. Vitagliano, P. Hyllus, I.L. Egusquiza, and G. Tóth, Spin squeezing inequalities for arbitrary spin, Phys. Rev. Lett. 107,
240502 (2011).

Colloquium 30.05.2013; 10:15 h; Room D 326

Prof. Dr. Klaus Sengstock
Universität Hamburg
Institut für Laserphysik und Zentrum für Optische Quantentechnologien

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Magnetism without magnetism: Different regimes of magnetic like quantum gas physics

Abstract: The talk will discuss different regimes of 'magnetism' in the physics of quantum gases. Starting from macrsocopic coherent spin dynamics in fermionic and bosonic quantum gases the talk will also address regimes of magnetsim fully without magnetic interactions. In this context artificial gauge fields recently attracted enormous amount of attention as they will allow to mimic fundamental physics like the behavior of condensed matter in extremely strong magnetic fields (e.g. the famous Hofstetter butterfly) up to QCD-like physics.

Colloquium 06.06.2013; 14:00 h; Room D 326

Prof. Dr. Nathan Goldman
Center for Nonlinear Phenomena and Complex Systems
Universit´e Libre de Bruxelles , Belgium

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Imaging Topological States in Ultracold Atomic Gases

The recent experimental realization of synthetic magnetic fields and spin-orbit couplings for ultracold (neutral) atoms opens the attractive possibility to engineer a wide family of topological quantum phases. In such arrangements, one indeed expects to create quantum Hall liquids and topological insulating phases, in a highly controllable and clean environment. However, measuring unambiguous signatures of these quantum phases, such as non-trivial topological order or the presence of current-carrying edge states, remains a fundamental issue for the cold-atom community.
In this talk, I will review the topological phases that could be realized in cold atomic gases. I will discuss the possibility to measure topological properties in these systems through available observables]. In particular, I will present efficient methods allowing for the detection of topological edge states in optical lattices.

Colloquium 20.06.2013; 10:15 h, Room D 326

Prof. Dr. Jakob Reichel
Laboratoire Kastler Brossel de l'E.N.S.
Institut Universitaire de France

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Creation and tomography of entangled states with up to 40 atoms in a cavity

We have created W states (Dicke states) of up to 40 atomic pseudospins and analyzed them by implementing a measurement of the Husimi distribution. State preparation and tomography are both based on optical cavity quantum electrodynamics. They take advantage of the exceptional properties of fiber Fabry-Perot cavities recently developed in our group.