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



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.


"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]

“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). [more]

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 [more]

“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." [more]

"Otto Stern: the nearly forgotten pioneer of atomic, molecular, and nuclear physics."

"Otto Stern is one of the great pioneers of modern atomic, molecular and nuclear physics. In 1943 he received the Nobel prize in physics for his development of the “Molecular Beam Method” and his “Measurement of the Magnetic Moment of the Proton”. The molecular beam method allowed physicists and chemists for the first time to perform experiments on single isolated atoms or molecules and determine inner properties of atoms and nuclei. For the exploration of the quantum world his invention has an importance similar to Gutenberg’s invention of single separated letters for printing of books. Stern was 81 times nominated for the Nobel prize in physics more than Planck, Einstein or any other of the great pioneers. Based on Sterns invention the Maser, the Atomic clock, the nuclear magnetic resonance etc. were developed. In 1933 Stern was forced to emigrate to the US since he was Jewish." [more]

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