Integrated Calendar

Vision is inarguably the most dependable of the five senses. The retina contains light sensing protein receptors (rhodopsins) that incorporate a small polyene molecule derivative of vitamin A, known as 11-cis-retinal. Major clues on understanding the visual cycle have been established through the design of variations of the vitamin A light absorbing molecule, some of which will be presented. A detailed understanding of the inner workings of rhodopsin is not only critical from the stand point of solving mysteries of visual diseases, like Age-related Macular Degeneration (the leading cause of blindness), but also serves as a well established model for elucidating the mechanism of other G-protein coupled receptors (GPCRs). Furthermore, we show that the value of light absorbing molecules expands beyond vision and can be used to trigger neurons thereby aiding the delineation of complex neural networks.

High precision spectroscopy of few-electron atoms and ions is strongly motivated by the need to test fundamental theory (e.g., quantum electrodynamics) in simple systems, amenable to precise calculation for comparison with experimental measurement. Additionally, transitions from the ground state are most susceptible to both QED and nuclear structure effects, making them appealing as tools for testing nuclear structure theory. The frequencies of transitions from the ground state in many such systems reside in the extreme ultraviolet range of the electromagnetic spectrum (XUV, wavelengths of 10-120 nm). However, spectroscopic resolution in the XUV is severely limited by the availability of appropriate sources of XUV radiation. In this talk I will discuss our experimental method of generating an XUV frequency comb laser, and our progress in scaling up the power of this laser in order to enable the highest spectroscopic precision in the XUV to date.

I will present experimental results on magnetic quantum fluids. These consist of a dilute Bose-Einstein condensate of dysprosium atoms, the most magnetic stable element. They allow to study the many-body consequences of the anisotropic and long-range dipole-dipole interaction, benefitting from the control tools of ultracold atomic physics.
First, we have observed in this system an unanticipated phase-transition between a gas and a liquid, characterized by the formation of self-bound droplets [1-3]. It forms in a parameter region where the existing theory, based on the mean-field approximation, predicted a mechanical collapse of the gas. We showed that the repulsive beyond meanfield corrections prevent the collapse and are responsible for the stabilization of the liquid [2]. These corrections arise from quantum fluctuations (zero-point motion) of the collective modes (Bogolyubov sound modes) in the quantum fluid.
In recent work we show that in constrained geometries, the ground-state is selforganized (left image). Studying these geometries experimentally, we indeed observe stable self-organized ‘stripe’ phases (right image), likely in metastable excited states. I will discuss the prospects for a strange kind of supersolidity in this system. In other experiments we study the effect of a rotating magnetic field on a quantum droplet, as a tool for the study of the different low-lying collective modes of the system.

[1] Observing the Rosensweig instability of a quantum ferrofluid, H. Kadau, M. Schmitt, M. Wenzel, C. Wink, T. Maier, I. Ferrier-Barbut, and T. Pfau, Nature 530, 194 (2016).
[2] Observation of quantum droplets in a strongly dipolar Bose gas, I. Ferrier-Barbut, H. Kadau, M. Schmitt, M. Wenzel, and T. Pfau, Phys. Rev. Lett. 116, 215301 (2016).
[3] Self-bound droplets of a dilute magnetic quantum liquid, M. Schmitt, M. Wenzel, F. Böttcher, I. Ferrier-Barbut and T. Pfau, Nature 539, 259 (2016).

‘Biomimetic Chemistry’ presents a conceptual approach to the art of model building attempting to imitate the activity of a biological system by emphasis on the function of a substrate rather than on its detailed molecular structure.
In the talk today I will center on the approach, governing the fundamental phenomenon of molecular recognition. The end goal is to formulate a set of rules essential to the design of molecules matching a specific biological system. Microbial iron-carriers, Siderophores, provide a useful platform for studying these principles. Several series of ferrichrome biomimetic analogs varying in length and polarity of the chains separating between the tripodal scaffold and the pendent FeIII chelating hydroxamic acid groups were prepared and studied. Microbial growth promotion was conducted on bacteria (E. coli, and P. putida) and fungi (U. maydis). These studies show a wide range of siderophore activity: from a rare case of species-specific growth promotor in P. putida to an analog with broad-spectrum activity matching ferrichrome in cross-phylum activity and uptake pathway. A fluorescent conjugate, to the broad-rang analog, provide clear images of the iron-free siderophore final destination in bacteria (periplasmic space) vs fungi (cytosol) mapping distinctly new therapeutic targets. Quantum Dots (QD) decorated with the most potent ferrichrome (FC) analog provided a tool for immobilization of FC-recognizing bacteria. Bacterial clusters formed around QDs, provide a platform for their selection and concentration.
The fascinating field of lanthanide-clusters will be introduces and their unique properties describe, possible future opportunities and application will be discussed.