לוח שנה משולב

Controlling the interaction of light and matter is the basis for diverse applications ranging from light technology to quantum information processing. Nowadays, many of these applications are based on nanophotonic structures. It turns out that the confinement of light in such nanostructures imposes an inherent link between its local polarization and its propagation direction, also referred to as spin–momentum locking of light [1]. Remarkably, this leads to chiral, i.e., propagation direction-dependent effects in the emission and absorption of light, and elementary processes of light–matter interaction are fundamentally altered. For example, when coupling plasmonic particles or atoms to evanescent fields, the intrinsic mirror symmetry of the particles’ emission can be broken. In our group, we observed this effect in the interaction between single rubidium atoms and the evanescent part of a light field that is confined by continuous total internal reflection in a whispering-gallery-mode microresonator [2]. In the following, this allowed us to realize chiral nanophotonic interfaces in which the emission direction of light into the structure is controlled by the polarization of the excitation light [3] or by the internal quantum state of the emitter [4], respectively. Moreover, we employed this chiral interaction to demonstrate an integrated optical isolator [5] as well as an integrated optical circulator [6] which operate at the single-photon level and which exhibit low loss. The latter are the first two examples of a new class of nonreciprocal nanophotonic devices which exploit the chiral interaction between single quantum emitters and transversally confined photons.

References
1 K. Y. Bliokh, F. J. Rodríguez-Fortuño, F. Nori, and A. V. Zayats, Spin-orbit interactions of light, Nat. Photon. 9, 796 (2015).
[2] C. Junge, D. O'Shea, J. Volz, and A. Rauschenbeutel, Strong coupling between single atoms and non-transversal photons, Phys. Rev. Lett. 110, 213604 (2013).
[3] J. Petersen, J. Volz, and A. Rauschenbeutel, Chiral nanophotonic waveguide interface based on spin-orbit coupling of light, Science 346, 67 (2014).
[4] R. Mitsch, C. Sayrin, B. Albrecht, P. Schneeweiss, and A. Rauschenbeutel, Quantum state-controlled directional spontaneous emission of photons into a nanophotonic waveguide, Nature Commun. 5, 5713 (2014).
[5] C. Sayrin, C. Junge, R. Mitsch, B. Albrecht, D. O'Shea, P. Schneeweiss, J. Volz, and A. Rauschenbeutel, Nanophotonic Optical Isolator Controlled by the Internal State of Cold Atoms, Phys. Rev. X 5, 041036 (2015).
[6] M. Scheucher, A. Hilico, E. Will, J. Volz, and A. Rauschenbeutel, Quantum optical circulator controlled by a single chirally coupled atom, Science 354, 1577 (2016).

Autism Spectrum Disorder is a heterogeneous condition characterized by deficits in social interactions and repetitive behaviors/restricted interests. Mouse models based on human disease-causing mutations provide the potential for understanding associated neuropathology and developing targeted treatments. Genetic, neurobiological and imaging data provide convergent evidence for the CNTNAP2 gene as a risk factor for autism and other developmental disorders. First, I will present data from my postdoctoral work demonstrating construct, face and predictive validity of a mouse knockout for the Cntnap2 gene, providing a tool for mechanistic and therapeutic research. In fact, through an in vivo drug screen in this model we found that administration of the neuropeptide oxytocin dramatically improves social deficits. Strikingly, reduced neuropeptide levels in this model seemed to account for the behavioral response. Last, I will present ongoing work in my lab evaluating the oxytocin system and related neurotransmitters in this model. Alterations in the oxytocin system and/or dysfunction in its related biological processes could potentially be more common in autism than previously anticipated.

My research focuses on the effects of interspecific competition on diversity and composition of herbaceous plant communities I developed a theoretical model that incorporates size-asymmetric competition into the classical resource competition model of Tilman (1982). The model shows that size-asymmetric light competition is a necessary and sufficient condition for explaining species loss under high levels of soil resources. The model’s predictions were tested in a Mediterranean annual community. For this purpose I developed a novel method for quantifying the size-asymmetry of light partitioning under field conditions. The experimental results were fully consistent with the predictions of the theoretical model. In addition I analyzed global scale data for testing the applicability of my models in various ecosystems. The results of the analysis provide further support for my theoretical and experimental findings.

The basic motivation for our work is to understand how charge is transported on an atomic spatial and attosecond time scale. Strong-field ionization in the dipole approximation (i.e. tunnel ionization) is much faster than the group delay of the electron wavepacket (i.e. Wigner delay), whereas photoemission from atoms can typically be described by the Wigner delay - but not in all cases. For example autoionization resonances in the continuum can change the ionization delay. Moving to condensed matter we have investigated the escape time of photoemitted electrons from metal surfaces such as Ag, Au and Cu. We want to address the question about the correct escape velocity of the electons and their ability to “feel” the periodic crystal potential on a attosecond time and an atomic length scale. Our most recent experiment can confirm an upper limit of around 300 attosecond over a distance less than 2 atomic layers during which an electron can assume its effective mass. Furthermore femtosecond charge transport modulation driven by a transient electric field in the petahertz regime have been observed in diamond and can be explained by the dynamical Kranz Keldysh effect (DFKE). State-of-the-art numerical calculations reveal that only a small number of transitions give rise to the observed effects and that the more classical intra-band transitions dominate the response over inter-band transitions.