Colloquia


Colloquia

We plan to return partly to in-person talks. These talks will be held in the interim lecture hall B 0.32 at MPQ and can additionally be attended online. Some talks remain online only.

2G regulations apply to in-person talks, i.e. every time you wish to participate in person, you will have to prove, e.g. with the CovPass-App, that you are vaccinated or recovered.Whether facemasks have to be worn inside the lecture hall will be communicated in the the e-mail announcement for each talk separately. In any case, you will need a medical facemask in the hallway. Audience not affiliated with MPQ are welcome to join in person as long as they meet 2G criteria.

Details on how to participate online are distributed via the mailing lists [wiss-mpq] and [Mpq-colloquium-stream]. To receive this information, please register using the adjacent link.

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

"We have studied short pulse laser ionization (< 7 fs, 750 nm) and excitation with polarization-gated laser pulses. The laser pulse used is composed of a circular section at the beginning and the end of the pulse and an experimentally-defined linearly polarized central part. Due to quantum mechanics selection rules (Dm ±1), multiphoton excitation of Rydberg states with high angular momentum are only possible with linearly polarized light. We show that polarization gating allows us to study excitation and ionization with quasi sub-cycle laser pulses. The method allows us to determine the shortest temporal window needed for the excitation processes. We have used polarization gated pulses to measure non-sequential ionization as a function of the gate duration." [more]
"Nanomechanical resonators are freely suspended, vibrating bridges with nanoscale diameters. These nanostructures are receiving an increasing amount of attention, both in fundamental experiments addressing the foundations of quantum mechanics and in sensing applications, and show great promise as linking elements in future hybrid nanosystems. A realization of this potential is however based on the development of not only nanomechanical systems of high mechanical quality factor but also suitable control techniques. Here I will review recent progress towards these goals, focussing on dielectrically controlled pre-stressed silicon nitride string resonators. In particular I will address the dynamics of two strongly coupled nanomechanical modes which can be described as a classical two-level system, adopting the well-known Bloch sphere picture. Analogous to the coherent control of two-level systems in atoms, spin ensembles or quantum bits, electromagnetic pulse techniques are employed to demonstrate full Bloch sphere control via Rabi, Ramsey and Hahn echo experiments. Our experiments not only enable deep insights into the limiting mechanisms for decoherence in nanomechanics, but also open a pathway towards single phonon control after a series of ground-breaking experiments on ground state cooling and non-classical signatures of nanomechanical resonators in recent years." [more]
"We demonstrate a robust photon detector which does not rely on photon absorption. Instead, impinging light is reflected off an optical resonator containing a single atom in a superposition of two states. Upon reflection of a single photon, the phase of the superposition state is flipped, which unambiguously allows us to nondestructively detect the photon. The presented single-photon nonlinearity paves the way towards photonic quantum gates and the preparation of novel quantum states of light." [more]
"Rydberg atoms provide a way to achieve controlled long-range interactions in many-body systems. In our setup we implemented an optical detection technique for Rydberg atoms with sub-micron resolution, which allows for the measurement spatial correlations in strongly interacting collective states of Rydberg atoms. We prepare a two-dimensional system of ground state atoms in an optical lattice and laser couple them to a Rydberg state. The Rydberg atoms interact via the van der Waals force, which extends over approximately half the system size, thereby leading to strong correlations. Guided by numerical optimization we found laser sweeps that created self-organized many-body states with spatially ordered Rydberg excitations. The initial ground state atom configuration is crucial for the success of the sweeps. We developed a preparation technique based on local addressing in an optical lattice that allows for the preparation of sub-shot-noise initial atom numbers. The developed techniques might allow for the deterministic preparation of ordered fock states of Rydberg atoms and the investigation of their coherence properties." [more]
"Photonic lattices are created by the inference of light in a complex way, and therefore represent an enabling technology for diverse applications as trapping atoms or optically tweezing nanoparticles, patterning in holographic lithography, and creating artificial matter as photonic crystals. In my presentation, I will show that by tailoring complex light landscapes as e.g. nondiffracting, self-similar or vortex-bearing light fields, or by randomizing these light fields, the next generation of artificial functional materials can be created as well as novel light routing and localization schemes can take place in these optically-created structures. Moreover, these light fields open new horizons in optical micromanipulation of artificial and biophybrid nanorobots." [more]
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