Applied Physics / Physics Colloquium

Astrophysical observations give overwhelming evidence for the existence of dark matter. Several theoretical particles have been proposed as dark matter candidates, including weakly interacting massive particles (WIMPs), axions, and more recently, their much lighter counterparts. However there has not yet been a definitive detection of dark matter. One group, the DAMA collaboration, has asserted for years that they observe a dark matter-induced annual modulation signal in their NaI(Tl)-based detectors. Their observations seem to be inconsistent with those from other direct detection dark matter experiments under most assumptions of dark matter. In this talk I will describe the current status of the debate and the world-wide experimental effort to test this extraordinary claim. I will report the recent results from the COSINE-100 experiment and our progress toward resolving the current stalemate in the field.

Quantum coherence can now be observed for longer than 100 microseconds in superconducting chips containing tens of physical qubits comprised of Josephson tunnel junctions embedded in resonant microwave circuitry. Combining such long-lived coherence with quantum-noise-limited, broadband detection of weak microwave signals has enabled the realization of nascent quantum processors suitable for executing shallow-circuit quantum algorithms with modest gate counts and minimal error mitigation. As an example, I will describe the implementation of a hybrid quantum-classical variational eigensolver with superconducting transmon qubits to determine the ground and excited states of simple molecules with near-chemical accuracy, and a teleportation protocol using ternary logic to simulate scrambling processes in black holes.

Although our physical world is 3+1 dimensional, curiosity has always driven scientists to study higher dimensional physics. The classic examples of such studies include the 4+1 dimensional generalization of quantum Hall state, and the "periodic table" of topological insulators in all dimensions. These studies are of pure theoretical interests only until last year, when a 4+1 dimensional topological insulator was realized in cold atom systems using the "synthetic techniques". The same technique allows us to explore even higher dimensional states of matter experimentally. In this talk we will discuss the interaction effects in these "synthetic topological insulators" in high dimensions. We realize that the generic interaction in this system takes a special form which is very different from ordinary condensed matter systems, and it has strong implications on the classification and phenomena of these synthetic topological insulators.

To most physicists, almost everything about evolution is puzzling. What determines how much complexity can — and has — evolved? Why is there so much biological diversity on all scales of differences? How could evolution select for future "evolvability"? Why doesn't evolution get slower and slower? One of the roles of theory is to frame questions — or at least limited versions of them — more precisely. And another is to reduce — or redirect — puzzlement by developing and analyzing simple caricature models to see what should be expected rather than be surprising. This talk will outline some recent progress in these directions, particularly by statistical physics ways of thinking.

The laser increased the intensity of light that can be generated by orders of magnitude and thus brought about nonlinear optical interactions with matter. Chirped pulse amplification, also known as CPA, changed the intensity level by a few more orders of magnitude and helped usher in a new type of laser-matter interaction that is referred to as high-intensity laser physics. In this talk, I will discuss the differences between nonlinear optics and high-intensity laser physics. The development of CPA and why short, intense laser pulses can cut transparent material will also be included. I will also discuss future applications.

Inside a cell, thousands of different genes function collectively to give rise to cellular behavior. Understanding the emergent behaviors of cells requires imaging at the genomic scale, which promises to transform our understanding in many areas of biology, such as regulation of gene expression, development of cell fate, and organization of distinct cell types in complex tissues. We developed a genomic-scale imaging method, MERFISH, which allows simultaneous imaging of hundreds to thousands of genes in individual cells and facilitates the delineation of gene regulatory networks, the mapping of molecular distribution inside cells, and the mapping of distinct cell types in complex tissues. We have also extended this approach to image numerous genomic loci and trace the 3D structure of chromosomes in single cells. I will describe the technology development of MERFISH and its applications, focusing on generating the cell atlas of complex tissues and mapping the 3D organization of the genome. 

In this talk I will describe our ongoing effort at the University of Chicago to explore exotic models of condensed matter using materials made of light. Starting with a quick discussion of "light as matter," I will then explain how we imbue photons with the essential attributes of a material particle: mass, charge, and interactions. Along the way, I will introduce the two "flavors" of photons that we employ for our photonic matter: optical photons trapped in Fabry-Perot cavities, and microwave photons trapped in superconducting resonators or transmon qubits. Finally, I will describe the first two materials that have emerged from our interacting photons: a Mott insulator of microwave photons and a topological fluid of optical photons. More broadly, building materials from light impacts both (a) the kinds of matter that can be assembled, and (b) the assembly process itself, providing a new window on the physics of correlated quantum matter.

Computational imaging involves the joint design of imaging system hardware and software, optimizing across the entire pipeline from acquisition to reconstruction. Computers can replace bulky and expensive optics by solving computational inverse problems. This talk will describe new microscopes that use computational imaging to enable 3D, super-resolution and phase imaging with simple and inexpensive hardware. Our reconstruction algorithms are based on large-scale nonlinear non-convex optimization. Applications span optical bioimaging, X-ray lithography and atomic-resolution electron microscopy.

Black holes have been instrumental in paving the way toward a quantum theory of gravity. Their elegant mathematical formulation has revealed that black holes behave as thermodynamic objects, which subsequently motivated the holographic principle. Its concrete realization, the gauge/gravity duality, offers a framework for elucidating the fundamental nature of spacetime, once we understand the map between the two sides of the duality sufficiently well. Research over the last decade has offered tantalizing hints that quantum entanglement plays a foundational role, ushering in more mysteries. This talk will give a broad-brush perspective on these themes and motivate considering a time-dependent context in order to gain further insight.

Our friend, Professor Shoucheng Zhang, passed away on December 1, 2018. This was a great loss for the entire physics community.

To honor Shoucheng and to celebrate his remarkable science and life, a Memorial Workshop from May 2-4, 2019 is being held.

Shoucheng has influenced many of us deeply with his great enthusiasm and unique talent for discovering the beauty and simplicity in physics. We feel that the best way to remember him is to dedicate to him a lively workshop with exciting lectures and a lot of fruitful discussion.