# Research Projects

### Summer 2023 Research Projects are in the following areas of Physics:

• Elementary Particle Physics
• Physics of Soft and Living Matter / Biophysics
• Condensed Matter Physics
• Gravity (Theory)
• Astronomy

RESEARCH PROJECTS

The MilliQan experiment: searching for fractionally charged particles at the Large Hadron Collider  (by Professor David Stuart,  Experimental Particle Physics)

Understanding the dark matter observed to dominate the mass of the universe is a key goal of particle physics and has led to models for a dark sector of new particles. Mixing between the photon and a dark sector photon would give dark sector particles a suppressed coupling to the photon which would manifest as fractionally charged particles. A new experiment, called MilliQan, is searching for production of particles at the LHC with charges down to a thousandth of the electron charge. The detector elements consist of scintillator bars with photo-multiplier tubes readout by waveform digitizers. The intern will be trained in the operation of the detector and then monitor the experiments operation and analyze its data. They will meet regularly with Prof. Stuart and graduate students working on the project and also present progress at weekly group meetings.

New Detector Technologies for Neutrino Physics (by Professor David Caratelli,  Experimental Particle Physics)

Neutrinos are one of the least understood fundamental particles. Because of how rarely they interact, we go to great lengths to devise experimental setups that can record their interactions to allow the study of their properties and their role in our universe’s evolution. Detectors that rely on liquid noble elements such as argon are widely used to image interactions of feeble neutrino signatures. This project will contribute to the development of new technologies that aim to enable the observation of rare neutrino interactions with lower energy thresholds and improved resolution compared to existing technologies. The work will consist of simulation studies aimed to understand the response of different detector setups to the signature of MeV-scale energy neutrino interactions, and include studies of detector optimization and performance to deliver quantifiable metrics for design requirements. Opportunities for data analysis and contributions to hardware development in the laboratory may also be available. This work will contribute key input for next stages in detector development. Prior experience working in a research laboratory is not required, but programming skills in python and C++ will be valuable in carrying out the project. Throughout the course of the project, the intern will further familiarize themselves with general principles of experimental particle physics detection methods.

Corkscrew defects in quantum gravity (by Professor Don Marolf, Gravity Theory)

Cutting a wedge out of a piece of paper and taping the ends of the wedge together creates a cone.  The tip of the cone is characterized by the fact that a small drawn on the cone and centered around the tip has Circumference C less than $2\pi r$ where $r$ is the distance from the tip of the cone to the circle.  In a general curved space, points of this sort are said to lie on a conical singularity.  Such conical singularities have recently been shown to play important roles in the understanding of black hole entropy, and in the path integral formulation of quantum gravity.  A natural generalization in higher dimensions is the `corckscrew defect,' exemplified by considering flat 3-dimensional space in polar coordinates $(\rho, \theta, z)$, removing the wedge $0 \le \theta \le \Delta$ for some $\Delta$, and identifying the boundary of the wedge at $\theta=0$ with the boundary at $\theta = \Delta$ under a map that also shifts $z \rightarrow z + \lambda$  for some constant $\lambda$.  This project will focus on understanding such corkscrew defects, and on building tools comparable to what have been created for conical defects for applications in quantum gravity.

Mapping the forces that shape organs (by Professor Sebastian Streichan, Physics of Soft and Living Matter)

Developmental biology has established principles of how the body plan is laid out, morphogens setup axes, and gene expression patterns determine cell fates. Yet, how shape is determined remains elusive. For a truly predictive framework of organ shape, molecular investigation must be extended by model driven quantitative analysis of tissue dynamics at the organismal level. Recent advances in light microscopy have enabled in toto live imaging of embryogenesis at high spatiotemporal resolution. However, light scattering in the often opaque specimen results in image quality degradation. This intern project will focus on improving image quality by 1) matching refractive index of mounting media with the sample, and 2) rejecting out of focus scattering light on the detection arm. To this end, the intern will 1) determine the refractive index of Drosophila melanogaster embryos at various stages of development, and 2) characterize signal improvement from using light-sheet mode detection. This project is suitable for all level interns, and will expose the intern to cutting edge science at the interface of physics and biology, advanced optics concepts, and a rigorous quantitative approach to morphogenesis.

“Filming” proteins in action (by Professor Mark Sherwin, Experimental Condensed Matter Physics / Physics of Soft and Living Matter)

Proteins are the molecular machines that power life as we know it.  The rapidly-growing protein data bank now holds more than 150,000 protein structures.  However, knowing their static structure is not sufficient.  To fully understand the operation of proteins as machines, one must understand their triggered functional dynamics–how protein structures evolve in time after being triggered by an external event such as ligand docking, movement of a neighboring protein, or a change in voltage or light intensity.  Capturing these conformational changes in a biologically relevant environment is a grand challenge in biology.

For the last 15 years, in collaboration with the group of Prof. Songi Han (Department of Chemistry and Biochemistry), the Sherwin group has developed a “movie camera” to “film” proteins in action.  Please see the Sherwin group website for details. https://sherwingroup.itst.ucsb.edu/research/gd3/.  The “camera” is based on electron paramagnetic resonance at very high magnetic fields.

This project is at a very exciting stage—we are starting to see proteins move!  In collaboration with Profs. Max Wilson (Molecular and Cellular Biology) and Arnab Mukherjee (Chemical Engineering), both protein scientists, we have recently observed, by a new method we developed called “Time-Resolved Gadolinium Gadolinium Electron paramagnetic Resonance” (TiGGER), the unfolding of one helix from the photo-responsive protein AsLOV2 after a flash of light.  We are now in a position to begin to unravel in detail the cascade of molecular events that occurs after the flash of light is absorbed by the “chromophore” molecule embedded in the heart of the protein.  There are hypotheses as to how this proceeds, but no hard data.

The project is moving quickly, and it is difficult to predict where we will be at the time the internship begins.  At this time, a likely REU project looks like this:

1.     Measure the time evolution of the state of the chromophore in a variety of mutants of AsLOV2 by measuring how its absorption spectrum changes as a function of time after a flash of light under conditions that are nearly identical to those under which we perform TiGGER, and come up with a method to simply analyze the time-resolved data, possibly using methods like singular value decomposition.

2.     Participate in the TiGGER experiments, and work to correlate the time evolution of the chromophore spectrum with the time evolution of the TiGGER data.  These measures will give us important data to distinguish different hypotheses about the mechanism of protein action.

3.     Explore the development of a method to monitor the state of the chromophore after a flash of light AT THE SAME TIME as the EPR experiment is occurring. This will involve some optics, fibers, lasers, a monochromator, and some software.

Studies of superconductor/semiconductor hybrid nanostructures (by Professor Christopher Palmstrom, Experimental Condensed Matter Physics/Materials)

The combination of a superconductor with a semiconductor nanostructure have been predicted to be able to host exotic quasiparticles called Majorana Fermions. These particles have no charge and no mass and can be thought of as half an electron and are their own antiparticle. The undergraduate student will be involved with nanofabricating superconductor/semiconductor structures, in-situ selective area growth and deposition using molecular beam epitaxial growth processes. Once fabricated, the student will perform structural, chemical and electrical measurements on these structures using a variety of atomic scale tools including scanning tunneling microscopy, spectroscopy and cryogenic temperature magnetotransport. Students will be involved in investigation induced superconductivity and proximity effects. A related project involves studies of superconductor/semiconductor/superconductor heterostructures with the aim of making a merged element transmon by integrating the Josephson junction and capacitor used to form the qubit in superconductor quantum computers, resulting in a dramatic reduction in the physical size of the superconducting qubit by over three orders of magnitude.

Studies of topological Heusler compound thin films (by Professor Christopher Palmstrom, Experimental Condensed Matter Physics/Materials)

The electronic structure in topological materials have some electronic states where the electron spin and momentum are locked, resulting in electrons with opposite spin moving in opposite directions. This makes them ideal spintronic devices. Heusler compounds, a combination of three elements with specific crystal structure, can have a range of electronic properties depending on the combinations. The group’s research focuses on the growth of Heusler compounds by molecular beam epitaxy and investigations of their atomic, electronic, topological, and magnetic properties. These properties can be tuned chemically via the number of valence electrons. Examples include the half-metals Co2MnSi and Co2MnAl, the semiconductors NiTiSn and CoTiSb, the topologically non-trivial PtLuSb and PtLuBi, and Weyl semi-metal candidate Co2TiGe. The student will be involved in performing and analyzing angle resolved photoemission, scanning tunneling spectroscopy and magnetotransport measurements at cryogenic temperatures to determine the electronic band structure and identify topological surface states. The project will also involve exfoliating and integrating 2D insulators without exposing the samples to air for controlling the electronic properties by electrical gating.

Characterization of Young Galaxies Using the James Webb Space Telescope (by Professor Crystal Martin, Observational Astronomy)

Professor Martin studies galaxy formation and evolution, focusing on the physical processes that shape their star formation history. Her work often involves analyzing emission lines in galaxy spectra. Undergraduate researchers have measured spectral lines and derived galaxy redshifts, rotation speeds, outflow speeds, and chemical compositions. The summer of 2022 offers special opportunities to work with the recently launched James Webb Space Telescope, the new space telescope built to reveal the assembly of galaxies.  Simulated data from each instrument is already available, and the Early Release Science programs will provide observations to the entire science community this summer.  Experience with astronomical data or Python programming is valuable, but the exact project will be matched to the preparation level of the student.

Direct Imaging of Exoplanetary Systems (by Professor Max Millar-Blanchaer, Astronomy)

Using space-based telescopes and the world's largest optical telescope, combined with advanced cameras and observing techniques we are now able to directly take pictures of young giant exoplanets and the protoplanetary disk in which they form. Even then, the signal from a planet or disk is typically buried underneath the signal from the host star and subtracting off this light is a major challenge. Advanced data processing techniques are required to see the planets and/or disks. The summer intern will work with Millar-Blanchaer to analyze new and old data from the Hubble Space Telescope or Subaru telescope in order to image extra solar systems in formation. The project will involve extensive use of Python and is appropriate for students with moderate to advanced knowledge of the language.