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

kommende Kolloquien



Die Gastvorträge im Rahmen des MPQ-Kolloquiums finden von April bis Juli sowie von Oktober bis Januar jeweils dienstags um 14:30 Uhr statt.

Achtung! Ab Oktober 2017 finden die Vorträge, aufgrund der Bauarbeiten, vorübergehend im Interims-Hörsaal, Raum B 0.32 am Max-Planck-Instituts für Quantenoptik statt.

Ansprechpartner für die wissenschaftliche Organisation:

Dr. Stephan Dürr und Dr. Thomas Udem

Wenn Sie einen Vortrag im Livestream verfolgen möchten, ist es nötig, dass Sie sich in eine entsprechende Mailing Liste eintragen. Daraufhin erhalten Sie Instruktionen zum Empfang des Livestreams.


"Superconducting Quantum Circuits: Ultra-strong Light-Matter Interaction and Path Entanglement of Continuous-variable Quantum Microwaves."

"Superconducting nanocircuits behave in many aspects similar to natural atoms. Despite the fact that these so-called artificial atoms are huge compared to their natural counterparts, they have a discrete level structure and exhibit properties unique to the world of quantum mechanics. In the simplest case, these artificial atoms form quantum two-level systems, also called quantum bits. We have realized superconducting flux quantum bits where the quantum two-level system is formed by symmetric and anti-symmetric superposition states of persistent currents circulat-ing clock- and anticlockwise in a superconducting loop [1]. Coupling these flux qubits to on-chip superconducting microwave resonators gives rise to the prospering field of superconducting circuit quantum electrodynamics (circuit-QED), which allows us to study the fundamental inter-action between artificial solid-state atoms and single microwave photons as the basis for com-municating quantum information. We discuss the realization of circuit-QED systems operating in the ultra-strong coupling regime, where the atom-cavity coupling rate reaches a considerable fraction of the atom transition frequency [2]. We also address quantum state tomography of propagating microwaves using a novel dual path detection scheme [3]. We have used this scheme to demonstrate for the first time frequency degenerate path entanglement of continu-ous-variable propagating quantum microwave signals. To this end, we entangle two spatially separate modes of the same frequency using a hybrid ring beam splitter and detect the entan-glement by means of cross-correlation techniques. The input fields of the beam splitter are squeezed vacuum and vacuum, respectively, and the correlations are evaluated up to the fourth moments in amplitude.This work is supported by the German Research Foundation via SFB 631 and the German Excellence Initia-tive via the Nanosystems Initiative Munich (NIM)."[1] T. Niemczyk et al., Supercond. Sci. Techn. 22, 034009 (2009); F. Deppe et al., PRB 76, 214503 (2007).[2] T. Niemczyk et al., Nat. Phys. 6, 772-776 (2010); F. Deppe et al., Nat. Phys. 4, 686 (2008); T. Niemczyk et al., arXiv:1107.0810v1.[3] E. Menzel et al., Phys. Rev. Lett. 105, 100401 (2010); M. Mariantoni et al., Phys. Rev. Lett. 105, 133601 (2010). [mehr]

"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. [mehr]

"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." [mehr]

"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 [mehr]

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