ansprechpartner

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




kommende Kolloquien

Kolloquien

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. Verantaltungsort ist der Herbert-Walther-Hörsaal im Foyer des Max-Planck-Instituts für Quantenoptik.

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.

Monat:

"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]

"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." [mehr]

“A toolbox for delocalization experiments with atoms, molecules and clusters of atoms and molecules.”

"Recent experiments in Vienna have shown that large covalently bound complexes, composed of several hundred atoms, can be delocalized over hundred times their own size and maintain quantum coherence over many milliseconds , even when heated to several hundred Kelvin. Two major motivations are driving this research: Nanoparticle interferometry turns out to be optimized for testing new measures of quantum macroscopicity. We will discuss the molecular beam methods and coherent manipulation schemes that are required to push the current state-of-the-art by the next orders of magnitude where new bounds will be set to non-standard quantum models at the quantum-classical interface. Molecular interferograms are quantum nanorulers either in position space or in the time-domain They have an intrinsic force sensitivity down to the Yoctonewton level and are therefore well-suited for novel measurements of magnetic, structural, electronic and optical properties of molecules, clusters and other nanoparticles with widely delocalized quantum states in controlled external fields."1. K. Hornberger et al., Rev. Mod. Phys. 84, 157 (2012).2. S. Nimmrichter et al., Phys. Rev. A 83, 043621 (2011).3. S. Gerlich et al., Nature Communs. 2, 263 (2011).4. T. Juffmann et al., Phys. Rev. Lett. 103, 263601 (2009).5. S. Gerlich et al. Angew. Chem. Int. Ed. 47, 6195 (2008).6. S. Gerlich et al., Nature Phys. 3, 711 (2007).7. L. Hackermüller, NATURE 427, 711-714 (2004). [mehr]

The shadow of a single atom

We have performed absorption imaging of a single atom for the first time [1]. A trapped Yb+ atomic ion scatters light out of an illumination beam tuned to atomic resonance at 369.5 nm. When the beam is reimaged onto a CCD camera, we observe an absorption image of 440 nm diameter and 5% contrast. The absorption contrast is investigated as a function of laser intensity and detuning, and closely conforms to the limits imposed by simple quantum theory and known properties of our imaging system. Defocused absorption images provide spatial interferograms of the scattered light, permitting accurate retrieval of the amplitude and phase of the scattered wave. We measure a phase shift of >1 radian in the scattered light as a function of laser detuning, which may be useful in quantum information protocols. The interferograms point to the possibility of observing the focusing of light by a single atom.[1] Streed et al., accepted to Nature Commun [mehr]

“Phase-resolved THz spectroscopy.”

"The generation of coherent THz pulses from femto-second sources has enormously progressed during the last 10 years. The band-width, intensities, as well as the efficiency has increased by using advanced semiconductor emitters and non-linear processes. In this way the spectral range up to 100 THz can be covered by quasi single cycle THz pulses. This frequency range – previously inaccessible for time-resolved spectroscopy - is an important part of the electro-magnetic spectrum due to a large number of fundamental resonances. Vibrational and rotational resonances of molecules are attractive for chemical sensing (chemical fingerprint analysis) and spectroscopic imaging. In solids, the resonance energies of phonons, plasmons and impurity transition are within the THz range. In particular also the transition energies of semiconductor nano structures occur in the THz band.Time-resolved THz spectroscopy allows phase-locked measurements – in particular phase-resolved detection. We take advantage of this fine capability to study the dynamics of semiconductor nanostructures. Phase-resolved THz spectroscopy allows unique measurements of stimulated emission form Quantum-Cascade Lasers. The knowledge of the phase of the THz response provides fascinating insights into the quantum mechanical processes. The study of highly excited nanostructures allows the prediction for coherent control schemes for optoelectronic devices. Together with novel resonator concepts we are able to show THz “switching” and strong coupling to quantized transitions." [mehr]

 
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