Physics Department Colloquium

Abstract: The Dark Energy Spectroscopic Instrument (DESI) collaboration is conducting a 5 year redshift survey of 40 million extra-galactic sources over 14,000 square degrees of the northern sky. One of its primary goals is to measure the cosmic expansion history with baryon acoustic oscillations (BAO). I will present the measurement of BAO in galaxy, quasar and Lyman-alpha forest tracers from the first year of observation.

Abstract: The ability to measure what students are learning (or not) is a crucial component of crafting effective learning environments. In particular, low-stakes, standardized diagnostic assessments can provide a valuable tool for tracking student learning over time and between instructional approaches to identify effective strategies that improve students' understanding of core physics content.

When can isolated many body quantum systems fail to go to equilibrium under their own dynamics, and how robust can this 'ergodicity breaking’ be? This question has been a central theme of research in quantum dynamics and statistical mechanics over the past decade, and I will share with you some highlights, focusing on three key developments: many body localization, dynamics with multipolar symmetries, and dynamics with higher form symmetries. I will present the rich and exotic phenomena that arise in these three regimes, and how they may be realized experimentally.

Abstract: Laser-based measurement and control of atomic and molecular states form the foundation of modern quantum technology and provide deep insights to fundamental physics. The recent breakthrough of quantum-state-resolved thorium-229 nuclear laser spectroscopy marks the beginning of precision metrology for nuclear transitions. Using a state-of-the-art frequency comb in the vacuum-ultraviolet, we coherently excite the thorium nuclear clock transition and link its frequency directly to today’s most precise atomic clock based on strontium-87.

Abstract: I will review some modern applications of effective field theories outside their traditional particle physics domain. In particular, I will focus on spontaneous symmetry breaking for spacetime symmetries. The effective theories for the associated Goldstone excitations capture the low-energy/long-distance dynamics of a number of physical systems, from ordinary macroscopic media (solids, fluids, superfluids, supersolids) to more exotic cosmological ones.

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.

Abstract:

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.

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.

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.