Graduate student Bochao Xu, DEpartment of Physics, University of Connecticut

Scanning SQUID Investigation of Time-reversal Symmetry Breaking in Exotic Quantum Materials

Spontaneous breaking of time-reversal symmetry in condensed matter systems arises from correlated electronic arrangements leading to various quantum phenomena, such as ferromagnetism, unconventional superconductivity, and topological states of matter. However, these underlying electronic orders are often difficult to detect experimentally if the magnetism associated with the time reversal symmetry breaking is weak. In such cases, the subtle magnetization and complex domain structure call for investigation by experimental techniques with both high magnetic sensitivity and high spatial resolution. In this dissertation talk, I will discuss my exploration of time-reversal symmetry breaking in two systems: a magnetic Weyl semimetal and a Kagome material detected using scanning superconducting quantum interference device (SQUID) microscopy. Both materials exhibit intriguing magnetic structures which were not detectable by the bulk measurements. We show that the Weyl semimetal hosts a tunable heterogeneous domain structure that is likely linked to its unconventional electronic properties. Additionally, our local probe reveals a ferromagnetic-like state in the Kagome material system, contributing evidence to the highly controversial problem within the community regarding the existence of time-reversal symmetry breaking and its underlying mechanism in this material. These results highlight the significance of quantum sensing in advancing the frontier of new correlated materials, and showcase these materials as an ideal playground for studying the magnetism-electrons interplay.

Dr. Jon Curtis, UCLA

Multimode cavity control of ferroelectric fluctuations

Electromagnetic cavities and metamaterials have been used to great effect in the field of AMO physics and electrical engineering. By shaping the spatial, spectral, or polarization characteristics of the electromagnetic environment, the coherent interaction between light and matter can be focused and amplified, leading to phenomena such as lasing, the Purcell effect, the Casimir effect, and superradiance. In this talk I will show how these ideas may be extended and applied to solid state quantum materials. In particular, I will consider polarization fluctuations in a quantum paraelectric insulator, and consider their coupling to a Fabry-Perot type optical cavity. By using the full multimode continuum description of the system, I will show how the ferroelectric fluctuations respond in a local, spatially resolved manner. The presence of the cavity indeed is shown to renormalize the soft-mode frequency, with effects primarily confined to the surface, and thus for thin films this effect can be pronounced. The temperature dependence shows this effect only onsets at low temperatures, indicating its origin from quantum electrodynamics effects – in close analogy with the Casimir effect.

Prof. Alan Wuosmaa, Department of Physics, University of Connecticut

Exotic Nuclei - What are they, how do we study them and why we should care

Just over one hundred years after their discovery by Rutherford, the nuclei of atoms are the focus of considerable renewed interest. Only about 300 nuclear isotopes are stable and can be found in nature, but nearly 3000 nuclei that are stable with respect to proton or neutron emission have been artificially produced in the laboratory. Our understanding of the behavior of the nucleus has largely been guided by ideas developed by studying the nuclei that are stable, however for unstable nuclei with a very large imbalance between protons and neutrons (so-called “exotic nuclei”), these ideas are proving insufficient. The experimental data needed to refine our understanding of the nucleus can only be obtained by performing reactions with short-lived radioactive nuclei. Experiments with such beams are difficult, and introduce many technical challenges. The data they can provide, however, are important not only to understanding nuclear structure, but many other situations such as the violent environments found in exploding stars in the cosmos. I will discuss some of the background behind studies of the structure of exotic nuclei, some modern experimental methods, and prospects for the future.

Prof. Alicia Kollár, University of Maryland

Lattices in Circuit QED

The field of circuit QED has emerged as a rich platform for both quantum computation and quantum simulation. These systems exhibit a high degree of both spatial and temporal control which can be used to create synthetic lattice systems. Spatial lattices can be formed using periodic arrays of resonators. Combined with strong qubitphoton interactions, these systems can be used to study dynamical phase transitions, many-body phenomena, and spin models in driven-dissipative systems. I will show that lattices of coplanar waveguide (CPW) resonators permit the creation of unique devices which host photons in curved spaces, gapped flat bands, and novel forms of qubit-qubit interaction [1,2]. I will show that graph theory is the natural language for describing these microwave photonic systems and present preliminary data on the development of a new generation of CPW lattice devices with unconventional band structures. Periodic modulation in superconducting-qubit systems also provides a route to Floquet systems with topological band structures. I will present preliminary experimental steps toward the realization of a topological energy pump which can “boost” smaller non-clalssical states of light into larger ones [3].

[1] A. J. Koll´ar et al., Nature 45, 571 (2019).

[2] A. J. Koll´ar et al., Comm. Math. Phys. 376, 1909 (2020).

[3] D. Long et al., Phys. Rev. Lett. 128, 183602 (2022).

Dr. Edwin Pedrozo, MIT

Quantum Sensors and the Search for New Physics

The continuously improving performance of quantum sensors is enabling the exploration of fundamental physics with unprecedented precision. Notable examples of these systems include optical atomic clocks and atom interferometers, which are among the most precise devices ever invented by humankind. As a result, they are increasingly utilized in the search for new physics. The application of Atomic, Molecular, and Optical (AMO) Physics techniques to such inquiries in the realm of nuclear physics has been gaining attention in the current decade. The level of control and precision achievable in AMO tabletop experiments, especially with ultracold atoms, enhances the measurement capabilities in complex experimental systems that pursue tests of fundamental physics and symmetries, the search for the electron electric dipole moment (eEDM), and physics beyond the standard model. In this talk, I will explain how incorporating entanglement into these systems can further improve their measurement capabilities. Additionally, I will discuss several proposals that employ laser-cooled atoms and molecules in the search for physics beyond the Standard Model.

Prof. Roopali Kukreja, UC Davis

Imaging ultrafast and ultrasmall: Unraveling nanoscale electronic and magnetic behavior using time-resolved x-ray scattering

Ultrafast laser control of correlated materials has emerged as a fascinating avenue of manipulating magnetic and electronic behavior at femtosecond timescales. Ultrafast manipulation of these materials has also been envisioned as a new paradigm for next generation memory and data storage devices. Numerous studies have been performed to understand the mechanism underlying laser excitation. However, it has been recently recognized that spatial domain structure and nanoscale heterogeneities can play a critical role in dictating ultrafast behavior. In this talk, I will discuss methods and our recent results which capture material behavior at nanoscale lengthscales and femtosecond-nanosecond timescales. I will describe our recent experimental studies using emerging synchrotron techniques and free electron laser such as European XFEL and FERMI. In the first part of my talk, I will discuss our results on ultrafast magnetization dynamics where we uncovered a symmetry-dependent behavior of the ultrafast response. Labyrinth domain structure with no translation symmetry exhibit an ultrafast shift in their isotropic diffraction peak position that indicates their spatial rearrangement. On the other hand, anisotropic domains with translation symmetry do not exhibit any modification of their anisotropic diffraction peak position. In the second part of my talk, I will focus on x-ray imaging of correlated oxides and discuss spatially dependent ultrafast response observed in complex oxides such as rare-earth nickelates. These intriguing observation suggests preferential, texture-dependent paths not only for the transport of angular momentum, but also for structural rearrangements. These measurements provide us with a unique way to study and manipulate spin, charge and lattice degrees of freedom.

Speaker’s bio: Roopali Kukreja joined Materials Science and Engineering department at UC Davis as an Assistant Professor in Fall 2016. She received her B.S. in Metallurgical Engineering and Materials Science from the Indian Institute of Technology Bombay in 2008 and then her M.S. and Ph.D. degrees in Materials Science and Engineering from Stanford University in 2011 and 2014, respectively. Prior to her appointment at UC Davis, Kukreja worked as a postdoctoral researcher at the UC San Diego, with Profs. Oleg Shpyrko (Physics Department) and Eric Fullerton (Center for Magnetic Recording Research). Her research interests at UC Davis focuses on ultrafast dynamics in nanoscale magnetic and electronic materials, time resolved X-ray diffraction and imaging techniques, thin film deposition and device fabrication.

Prof. Gerald Dunne, Department of Physics, University of Connecticut

Scientific Communication

I will discuss the problem of preparing a scientific presentation (a paper, a talk, a proposal, …). This is a valuable skill that all aspiring scientists should make the effort to learn. It is difficult, but it is both valuable and enjoyable, and well worth the effort.

Prof. Steve Lamoreaux, Yale University

Title: TBA