The reconciliation of quantum field theory with general relativity is probably the greatest outstanding problem in fundamental physics. This is an old problem, and it has inspired a tremendous amount of fascinating work; however, the basic conflict between quantum mechanics and general relativity has not been resolved, and there is a natural expectation that quantum gravity effects should only become important in reactions where single-particle energies are comparable to the Planck scale, far beyond what could possibly be generated at any accelerators in the foreseeable future.  Therefore, if experimental evidence of quantum gravity is to be found, a different approach is needed.  One way to look for evidence of quantum gravity effects is to search for phenomena that cannot occur in either the standard model or general relativity, such as violations of fundamental symmetries like Lorentz and CPT invariances.  If either of these symmetries are found to be violated in nature, that would represent an incredibly important clue about what quantum gravity should look like.

Many of the most stringent tests of these symmetries come from comparisons made with complementary atomic clocks.  Dr. Altschul can mentor up to two REU students working on projects related to the analysis of existing and future atomic clock experiments.  While there have been numerous after-the-fact analyses of radio-frequency clock experiments, there has been far less work on similarly precise optical atomic clock experiments.  Using an established formalism, each REU student will look at one or more of these optical clock experiments and develop expressions describing the sensitivities of these experiments to the various forms of Lorentz and CPT violation that might exist in nature.  Taking part in some of the first steps in this effort, the students will work directly with Dr. Altschul (with a faculty-student meeting each morning to asses ongoing progress) and will also be collaborating with a graduate student to identify previous and upcoming optical spectroscopy experiments whose results may be interpreted as sensitive tests of exotic physics beyond the standard model, based on the studying the laboratory configurations, experimental precision, and the types and estimated sizes of the quantum-mechanical matrix elements involved.  To calculate the matrix elements, the students will learn to work with analytical and numerical approximations for atomic wave functions—including the Thomas-Fermi statistical model, which can be useful for the outer orbitals of many-electron atoms, and computer calculations programmed using Python or Mathematica, which may be needed to get reliable estimates of matrix elements involving more tightly bound orbitals.

Dr. Bazaliy is a condensed matter theorist working in the area of magnetism and spintronics.  He is doing research on the generation and propagation of spin currents and studies magnetic dynamics excited by spin torques.  These areas have possible applications in developing new types of computer memory and logic devices.  Working with Dr. Bazaliy, a REU student will participate in a project in the area of Floquet theory and Floquet control of novel materials.  The Floquet theorem predicts that the solution of the equations of motion for a quantum mechanical system with a monochromatically periodic Hamiltonian is given (by analogy to the Bloch theorem for spatially periodic crystal backgrounds) by a product of a periodic function of time and a Bloch-wave-like phase factor.  This result has recently led to proposals for Floquet engineering, the goal of which is to control and qualitatively change the properties and functions of materials that are exposed to pulsed or oscillating external fields.

This project could be a good fit for an undergraduate who has completed an introductory course in quantum mechanics. It will introduce the student to concepts widely discussed in current literature.  With Dr. Bazaliy's direct assistance, the student will become familiar with theoretical models describing Floquet-type behavior.  Depending on the regime, the solution of an approximate equation of motion, using a small number of Taylor series terms may be close to the actual solution, and the student will learn and practice techniques for recognizing which approximation schemes will be useful for studying a given system.  The project will then move on to its second focus: performing computer simulations of the behavior of selected periodically excited systems.

Dr. Thomas M. Crawford can host 1–3 undergraduate students in his laboratory to work on nanotechnology projects related to nanomanufacturing and magnetic-field-directed self-assembly.  Their projects would be done under the supervision of Dr. Crawford and each in collaboration with one or more graduate students in the lab.

One undergraduate-appropriate project employs dark-field, bright-field, and fluorescence microscopy to visualize in real time, in fluid, the assembly of magnetic nanoparticles onto magnetically-recorded nanotemplates.  By studying the dynamics of the assembly and the velocity distribution of nanoparticle motion, the student will assess how this distribution changes dynamically, as the nanoparticles are pulled from the fluid to the surface and assemble into sub-micrometer patterns.  This project will assess experimentally the relative importance of diffusive and thermal nanoparticle transport in comparison with motion driven by nano-patterned magnetic forces.  It is self-contained and optimal for completion over the timescale of a summer research experience, while presenting a challenging experience for an undergraduate student.

The second project involves nanomanufacturing diffractive optical elements and using a combination of light sources to study spectral responses of the nanomanufactured films.  Here an undergraduate will nanomanufacture a standalone diffraction grating built entirely from magnetic nanoparticles, and will then test that grating in an optical spectrograph test-bed.  In addition to studying diffracted spectra and how the spectra depend on the nanomanufacturing process, the student could move on to study changes in the film's optical properties in response to both thermal and magnetic stimuli.

A third project would involve using optical sources to study magnetic properties of novel quantum materials.  These include both reflected and scattered magneto-optical Kerr effect (MOKE) as well as the acquisition of first-order-reversal curves from the magnetization of quantum material alloys, nanoparticles, and nanofibers.  Additionally, Crawford's apparatuses include combining MOKE with second harmonic generation (SHG) to study non-centrosymmetric materials in addition to material surfaces and interfaces.

Large language models like ChatGPT are poised to become an essential component of education.  Dr. Crittenden aims to develop a system of interacting AIs that behave:  as a clone of the instructor, as a peer mentor, as a graduate-level tutor, and as a performance assessor, all of which will work together, talking to each other, to assist a hypothetical student taking a physics course.

Working directly with Dr. Crittenden, the REU student can be involved in every step of the project.  The student will learn multiple approaches to tuning the behavior of AIs including prompt engineering and Retrieval-Augmented Generation and the use of state-of-the-art AI system programming tools such as DSPy and LangChain to link multiple AIs together to form a system that assesses and responds to a hypothetical physics student.  The goal is a team of always-available guides and assistants to the physics student, tailored to each particular instructor's approach to every course, rather than the average response that simply asking ChatGPT directly gives.  There will be a great deal of flexibility in the particular tasks the REU student will work on, and no programming skill is required; AIs speak English and, moreover, they are quite capable of assisting with any Python code that needs to be generated.

Theoretical research led by Dr. Gudkov is related to testing the standard model of particle interactions and to the search for new physics in low-energy interactions. This includes theoretical studies of the feasibility of searches for manifestations of new physics beyond the standard model in fundamental neutron physics, with emphasis on fundamental symmetries and "exotic" interactions.  Research topics include studies of time reversal invariance violation (TRIV) in neutron-nucleus scattering, parity violating (PV) effects in nuclear interactions, and possible manifestations of new physics in neutron decays and in interactions of neutrons with nuclei.  The research program provides theoretical support to the experimental programs in fundamental neutron physics at the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory, the Japanese SNS at J-PARC, and the European Spallation Source, which are focused on the study of neutron properties, neutron β-decay, neutron-antineutron oscillations, and PV or TRIV effects.

A REU student working directly with Dr. Gudkov will learn basic approaches to the study of symmetries in particle and nuclear physics and will contribute to computer simulations of some proposed experiments.  Many parameters related to reactions involving neutrons and protons have, in recent years, been measured and evaluated by a number of different groups.  The student will work with this wealth of data to estimate the strengths of PV or TRIV effects observable in the next generation of proposed experiments, as functions of the neutron energies involved.

Prof. Rongying Jin’s research lies in the area of experimental condensed matter physics.  This is a highly interdisciplinary field requiring perspectives from physics, chemistry, materials science, and engineering.  The objective of her research is to apply the experimental tools of materials synthesis, compositional tuning, and crystal growth to address cutting-edge issues in quantum materials.  Her effort has been devoted to (1) the development of new quantum materials with intriguing properties (superconductivity, quantum magnetism, nontrivial topology, thermoelectrics, multiferroics, etc.); (2) the investigation of physical properties:  charge, spin, and heat transport, magnetization, specific heat, microscopic (magnetic force microscopy, scanning tunneling microscopy, transmission electron microscopy), and spectroscopic (angle-resolved photoemission, and neutron scattering) measurements; and (3) collaboration with theorists/computational scientists for atomic-level understanding of the observed phenomena.  Under the guidance of senior researchers (postdoctoral fellows and graduate students), REU researchers will have opportunities to participate in materials synthesis and/or physical properties measurements including electrical, magnetic, thermal, and thermodynamical properties.

Ultrafast optical control holds promise for tailoring electronic and structural properties of novel materials.  Recently, a stable photo-induced hidden state has been found in 1T-TaS₂, which is different from its equilibrium phase.  One feature of the hidden state is the observation of enhanced electrical conductivity, enabling novel all-electronic nonvolatile memory devices.  However, the structural features of the hidden state and their effects on the electronic structure have remained elusive.  Recent experiments, in which the Dr. Mu was involved, identified the coexistence of mixed chirality and a long-lived hidden state in 1T-TaS₂.  Specifically, it has been found that the top layer and the layer buried underneath support charge density waves (CDWs) with opposite chirality, thereby forming a twisted CDW bilayer with a moire pattern. From density function theory (DFT) calculations combined with unfolding techniques, Dr. Mu's group is aiming to address the structure-property relationship in this twisted CDW bilayer.

A specific seed project is designed for a REU student to contribute to this research area under Dr. Mu's immediate supervision.  The undergraduate participant will help to build the atomic models obtained from scanning tunneling microscope (STM) and x-ray measurements, which is the first but most important step for further electronic structure calculations.  Moire structures will be built by the undergraduate student, with tunable twist angles between the bilayer and different stacking cases. In addition, the undergraduate student will learn about the state-of-the-art DFT used to assess the basic physical properties of novel materials.

Particle theory research led by Dr. Petrov pertains to understanding the structure of the fundamental electroweak Lagrangian at the smallest scales and developing theoretical tools needed for the "clean" interpretation of results from experiments probing the origins of mass and CP-violation.  In recent years, Dr. Petrov has worked on various problems in the theory and phenomenology of strong, electromagnetic, and weak interactions.  REU research topics include studies of the properties of heavy hadrons, applications of effective field theories to problems in quantum chromodynamics (QCD), particle astrophysics, neutrino physics, and the physics of CP-violation.  The research program significantly overlaps with the current research interests of USC's experimental particle and nuclear physics groups.

A student will learn and apply numerical fitting techniques used in the studies of charmed meson decays under various flavor-SU(3)-breaking assumptions. The student's primary task would be to learn and apply fits of theoretical parameters describing meson decays to experimental data.  The fits produced by the student will be the main outcome of the summer project.

In 2010, high-precision studies of muonic hydrogen found notably smaller values for the proton charge radius than earlier results that have been extracted from elastic electron scattering data and through the spectroscopy of atomic hydrogen. The MUon Scattering Experiment (MUSE) at the Paul Scherrer Institute has been developed by an international collaboration of researchers to address this "proton-radius puzzle."  The experiment will measure elastic electron-proton and muon-proton scattering data with positively and negatively charged beams in a four-momentum-transfer range from 0.002 to 0.08 GeV².  Each of the four data sets will allow the extraction of the proton charge radius.  In combination, the data test possible differences between the electron and muon interactions and provide novel data on two-photon exchange effects in the scattering process.  Dr. Strauch is the spokesperson for the experiment.  His group has built two double-plane time-of-flight scintillator walls, veto detectors, and beam-line monitors for MUSE.  The present efforts include the development of a full Monte Carlo simulation of the experiment, the study of radiative corrections, and the analysis of calibration and first production data.

Three USC graduate and 15 undergraduate students have worked on research projects related to MUSE; three of them were REU students.  Topics for future REU students include a Monte Carlo simulation of the time response for the MUSE scintillation detectors, the improvement of the experiment model in the simulation, the study of background from particle scattering off inactive support structures in the experiment, the development of procedures to monitor and determine detector calibrations from production data, the improvement on the digitization of simulated data and comparison of the results with data, and analysis of time-of-flight data to determine the muon beam momentum.  These projects will be performed under the supervision of Dr. Strauch, with the collaboration of the graduate students in the experimental nuclear physics group.  The participants will also be part of meetings involving the other two faculty members in the group, as well as outside collaborators.

The main focus of Dr. Wu's laboratory is on the fabrication and optical study of hybrid nanostructures consisting of different material platforms including semiconductors, metals, multiferroic fibers, topological insulators, and ferroelectric polymers to unveil new properties for device applications and quantum information processing.  The main mode of investigating these hybrid systems is through the use of various optical techniques such as SHG, photoluminescence coherent pump-probe spectroscopy, etc. Current hybrid systems being studied include quantum dot/plasmonic hybrid structures, multiferroic nanowires, and thin films of PVDF (a ferroelectric polymer) embedded with plasmonic nanoparticles.

In Dr. Wu's lab, REU students will be able to select between two projects.  In the first project, interesting phase transitions in a variety of fascinating quantum materials, including superconductors, topological insulators, semi-metals, etc., will be investigated utilizing optical SHG polarimetry.  In the second project, transparent, flexible ferroelectic PVDF platforms will be used to support the fabrication of tunable photonic nanostructures.

A student working on the first project will first complete a week of rigorous training on how to handle and set up optical components (such as mirrors and lenses) safely and how to use them to excite and collect optical signals from a practice sample.  They will learn about the basics of material properties, such as crystal symmetries, and how they can be identified using SHG.  They will learn how to clean and prepare samples for optical measurements during the second week and will discover how to use x-ray diffraction to perform preliminary measurements in order to first identify the target crystal plane for SHG.  The majority of their time will be spent actively collaborating with a graduate student in Dr. Wu's group, collecting SHG data as a pair.  The REU student will also participate in the data analysis process, using programs like Igor, Python, and Mathematica.

A REU student interested in the second project will spend about two weeks training to use the NanoFrazor, a thermal scanning probe lithography instrument, which is used for nanopatterning.  After training, under Dr. Wu's direct supervision, the participant will go through the entire nanofabrication process in the SmartState Center's cleanroom environment, including:  sample cleaning, spin-coating thermal resist, designing and writing patterns with the NanoFrazor, depositing the patterns using e-beam deposition, and liftoff.  Once they are proficient on the NanoFrazor, they will learn to prepare ferroelectric polymer films and practice the process of transferring prepared nanopatterns onto the polymer platform.

Dr. Wu will be closely monitoring the progress of the REU students.  In addition to a traditional lab notebook, they will be expected to keep a Powerpoint research journal with thorough notes, illustrations, and graphs.  In addition to their experimental results, their research journals will include information gleaned from the scientific literature, which they will be reviewing with Dr. Wu's guidance.  During the weekly research group meetings and Zoom meetings with collaborators, they will present their overall progress and outcomes using the Powerpoint diaries. The students will attend the SmartState weekly journal clubs, where they will be exposed to the latest research on relevant topics.  In addition, they will be given the opportunity to present a journal article to the center members.  They can polish their scientific communication skills in a welcoming and encouraging environment during group meetings and journal clubs.