Seminar

Abstract: A new direction in topological quantum matter research is the exploration of the large class of nonsymmorphic metals which include glide symmetry operations in their space group (a glide gx =Mx.T is a mirror reflection Mx combined with a fractional translation T in the mirror plane). The layered material KHgSb is analogous to stacking graphene together with distinct ions in the A and B sublattices. A half-lattice translation between adjacent layers renders it nonsymmorphic. KHgSb has been predicted to feature double quantum spin Hall (QSH) surface states in addition to hourglass...

Light-matter interaction is at the heart of most optical processes we are familiar with such as absorption, emission and scattering. These are normally treated by assuming that the incident light does not significantly modify the underlying electronic states of the material it interacts with. The strong coupling regime consists of the extreme case where light-matter interaction is so strong that it must be treated non-pertubatively. Polaritons, the resulting mixed light-matter particles, can be the source of many unique phenomena. We will describe how these quasiparticles can be exploited...

How do fluids become turbulent as their flow velocity is increased? In recent years, careful experiments in pipes and Taylor-Couette systems have revealed that the lifetime of transient turbulent regions in a fluid appears to diverge with flow velocity just before the onset of turbulence, faster than any power law or exponential function. I show how this superexponential scaling of the turbulent lifetime in pipe flow is related to extreme value statistics, which I show is a manifestation of a mapping between transitional turbulence and the statistical mechanics model of directed percolation.  This mapping itself arises from a further surprising and remarkable connection: laminar and turbulent regions in a fluid behave as a predator-prey ecosystem. Such ecosystems are governed by individual fluctuations in the population and being naturally quantized, are solvable by path integral techniques from field theory. I explain the evidence for this mapping, and propose how a unified picture of the transition to turbulence emerges in systems ranging from turbulent convection to magnetohydrodynamics. 

Empirical evidence suggests that living neural networks operate near a continuous phase transition, conjectured to be an optimal point for information storage and processing. Applying theoretical approaches, however, is challenging since vital features of neural networks present numerous obstacles to the applicability of traditional statistical physics tools, many of which have not yet been adapted to neuroscience. I will describe a simple cellular automaton model which allows for the characterization of the out-of-equilibrium transition and demonstrates an explicit symmetry breaking due...

Interfaces between two distinct complex oxide materials can display ground states which diverge greatly from the parent compounds, making them a playground to establish emergent phenomena. Particularly intriguing are the so-called polar interfaces where a diverging electrostatic potential leads to charge transfer. The canonical polar interface between two insulating oxides, LaAlO3/SrTiO3, forms a two-dimensional electron liquid which superconductors at low-temperature and where the conductivity can be manipulated by changing the film surface. Here, I will demonstrate novel functionality at...

Preserving the quantum coherence of signals is of paramount importance for components utilized in quantum information processing, quantum computation and quantum measurement setups. In recent years a tremendous progress has been made in the development of quantum-limited components, such as reciprocal and nonreciprocal amplifiers, circulators and isolators. A promising way to design these devices is based on parametric modulation of coupled modes, where the required mode-mixing processes are realized by utilizing Josphson junction-based tunable couplers or via coupling to mechanical...