Dr. Stephan Dürr
Stephan Dürr
Group Leader
Phone: +49 89 3 29 05 - 291
Room: A 2.22
Prof. Dr. Thomas Udem
Thomas Udem
Phone: +49 89 3 29 05 - 282 // -257
Room: D 0.21 // D 0.39

next colloquium

  • The colloquium series will resume at the beginning of the next term in April/October.



Our series of Colloquium Talks takes place from October till January and from April till July, on Tuesdays, at 2:30 p.m..

Attention! Due to the recontstruction of the foyer at the MPQ talks will take place at the interims Lecuture Hall in Room B 0.32.

Scientific organization of the talks: Dr. Stephan Dürr and Dr. Thomas Udem

If you wish to view the live stream of the MPQ colloquium, please use the link to subscribe to the corresponding mailing list. Detailed instructions will be sent to all subscribers.


"Cavity QED with fiber Fabry-Perot cavities."

"Miniature, fiber-based Fabry-Perot cavities (FFPs) are enabling novel experiments in cavity quantum electrodynamics, with cold atoms as well as with solid-state emitters. We have used such an FFP cavity to create an entangled state in a small ensemble of about 20 atoms, extracted from a BEC on an atom chip. We also use the cavity to measure the Husimi distribution of this entangled multi-atom state. In will also describe a new experiment where an FFP cavity is used to prepare a Bose-Einstein condensate of exciton polaritons in a semiconductor quantum well. [more]

"Beyond Standard Optical Lattices: Topological Insulators and Frustrated Magnetism."

"The last years have witnessed dramatic progress in experimental control and refinement of optical potentials for ultracold atoms. Two major recent developments are the realization of synthetic gauge fields for neutral atoms,allowing the simulation of topologically nontrivial phases of matter, and the creation of frustrated lattice geometries such as triangular or Kagome. Particularly rich physics arises in the presence of multiple atomic species and strong interactions, which I will discuss for two different examples. 1) We consider a spinful and time-reversal invariant version of the Hofstadter problem which can be realized in ultracold atoms. In these experiments, an additional staggered potential and spin-orbit coupling are available. Without interactions, the system exhibits various phases such as topological and normal insulator, metal as well as semi-metal phases with two or even more Dirac cones. Using a combination of real-space dynamical mean-field theory and analytical techniques, we discuss the effect of on-site interactions and determine the corresponding phase diagram. In particular, we investigate the stability of topological insulator phases in the presence of strong interactions. We compute spectral functions which allow us to study the edge states of strongly correlated topological phases. 2) We study Bose-Bose mixtures on a triangular lattice, in the case of total filling one where geometric frustration arises for asymmetric hopping. We map out a rich ground state phase diagram including xy-ferromagnetic, spin-density wave, superfluid, and supersolid phases. In particular, we identify a stripe spin-density wave phase for highly asymmetric hopping. On top of the spin-density wave, we find that the system generically shows weak charge (particle) density wave order." [more]

"Rydberg blockade, slow light and interacting dark-state polaritons."*

"Interfacing light and matter at the quantum level is at the heart of modern atomic and optical physics and is a unifying theme of many diverse areas of research. A prototypical realization is electromagnetically induced transparency (EIT), whereby quantum interference gives rise to long-lived hybrid states of atoms and photons called dark-state polaritons. In my talk I will give a general introduction into the field of ultracold Rydberg gases, with special emphasis on recent developments towards nonlinear quantum optics and the observation of strong interactions between dark-state polaritons in an ultracold atomic gas involving highly excited (Rydberg) states. By combining optical imaging with counting of individual Rydberg excitations we probe both aspects of this atom-light system. Extreme Rydberg-Rydberg interactions give rise to a polariton blockade, which is revealed by a strongly nonlinear optical response of the atomic gas. For our system the polaritons are almost entirely matter-like allowing us to directly measure the statistical distribution of polaritons in the gas. For increasing densities we observe a clear transition from Poissonian to sub-Poissonian statistics, indicating the emergence of spatial and temporal correlations between polaritons. These experiments, which can be thought of as Rydberg dressing of photons, show that it is possible to control the statistics of light fields, and could form the basis for new types of long-range interacting quantum fluids." * Work performed in collaboration with Christoph Hofmann, Georg Günter, Hanna Schempp, Martin Robert-de-Saint-Vincent and Shannon Whitlock [more]

"Quantum properties of polariton fluids in semiconductor microcavities."

"Polaritons are very special quasi-particles, which are a mixture of matter and light. In a semiconductor microcavity exciton-polaritons arise from strong coupling between cavity photons and quantum well excitons (bound electron-hole states). What makes them very attractive is the possibility of combining the coherent properties of photons with the highly interacting features of electronic states. They have recently demonstrated unprecedented non-linearities, Bose-Einstein condensation and superfluidity.First, I will show that these nonlinearities can bring quantum optical effects, as well as polarization controlled optical gates, spin control and ultra-fast spin switching. In addition, due to their very low mass (~10-4 times that of the electron, inherited from their photonic component), polaritons also exhibit condensation and quantum fluid properties at temperatures of a few K. I will present our recent results, demonstrating superfluid motion of polaritons, which manifests itself as the ability to flow without friction when the flow velocity is slower than the speed of sound in the fluid. Cerenkov-like wake patterns, vortices and dark solitons are also observed when the flow velocity is varied." [more]

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