JILA Auditorium
Predicting and harnessing unusual quantum effects in condensed-phase chemical processes via a synthesis of machine learning, path integration, and enhanced sampling
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Abstract: Reliable theoretical prediction of complex chemical processes in condensed phases requires an accurate quantum mechanical description of interatomic interactions. If these are to be used in a molecular dynamics calculation, they are often generated “on the fly” from approximate solutions of the electronic Schrödinger equation as the simulation proceeds, a technique known as ab initio molecular dynamics (AIMD). However, due to the high computational cost of these quantum calculations, alternative approaches employing machine learning methods repre
Electron fractionalization in topological quantum materials
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Abstract: The emergence of quasiparticles with fractional charge and fractional statistics is an essential feature of fractional quantum Hall states, which occur in two-dimensional electron gas under a strong magnetic field. An interesting question is whether fractional electron states can form spontaneously in quantum materials without the external magnetic field.
Photon upconversion: getting molecules and nanocrystals to talk triplets
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Abstract: In order to harness the intrinsic ability of colloidal semiconductor nanocrystals to couple strongly with light, it is important to efficiently outcouple energy from photoexcited quantum dots (QDs), much like how nature uses molecular antennas to direct light during photosynthesis. This talk focuses on aromatic acceptor ligands for triplet-fusion based photon upconversion, where orbital overlap between the QD donor and molecular acceptor is critical for efficient energy transduction.
Symmetry, topology and electronic phases of matter
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Abstract: Symmetry and topology are two of the conceptual pillars that underlie our understanding of matter. While both ideas are old, over the past several years a new appreciation of their interplay has led to dramatic progress in our understanding of topological electronic materials. A paradigm that has emerged is that insulating electronic states with an energy gap fall into distinct topological classes. Interfaces between different topological phases exhibit gapless conducting states that are protected and are impossible to get rid of.
Waves of Topological Origin in the Fluid Earth System and Beyond
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Abstract: Symmetries and topology are central to our understanding of physical systems. Topology, for instance, explains the precise quantization of the Hall effect and the protection of surface states in topological insulators against scattering from disorder or bumps. However discrete symmetries and topology have not, until recently, contributed much to our understanding of the fluid dynamics of oceans and atmospheres.
Chemical Kinetics in Microdroplets
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Abstract: Over that last 10+ years there has emerged some evidence that when a reaction vessel is reduced to the micron-sized dimensions (e.g. droplets), bimolecular reactions speed up by many orders of magnitude. The mechanism(s) for rate acceleration in droplets remains unclear but has clear implications for understanding the chemistry of atmospheric aerosols. A key uncertainty in the interpretation of droplet kinetics is how to properly link reaction rates measured in beaker scale containers with those occurring in micron-sized spaces.
Programmable quantum sensing using ultracold atoms in 3D optical lattices
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Abstract: The creation of a matter-wave interferometer can be achieved by loading Bose-Einstein condensed atoms into a crystal of light formed by interfering laser beams. By translating this optical lattice in a specific way, the traditional steps of interferometry can all be implemented, i.e., splitting, propagating, reflecting, and recombining the quantum wavefunction. Using this concept, we have designed and built a compact device to sense inertial signals, including accelerations, rotations, gravity, and gravity gradients.