The Department of Physics at the University of Illinois at Urbana-Champaign is known for its collegial style of research—the “Urbana style”—that often involves collaborations across research areas and among theoretical and experimental physicists. Here is an inside glimpse of what some of our leading physicists are working on.
Spectrum - SPRING 2018
The Department of Physics at the University of Illinois at Urbana-Champaign is known for its collegial style of research—the “Urbana style”—that often involves collaborations across research areas and among theoretical and experimental physicists. Here is an inside glimpse of what some of our leading physicists are working on.
LIANG YANG
Nuclear Physics
JESSIE SHELTON
Particle Physics
ALEXEI AKSIMENTIEV
Biological Physics
VIRGINIA LORENZ
Atomic, Molecular, and Optical Physics
GREG MACDOUGALL
Condensed Matter
Physics
LIANG YANG
My research centers on understanding the fundamental properties of the neutrino, one of the most elusive and mysterious elementary particles in the universe. Neutrinos are tiny and have almost no interactions with ordinary matter. Physicists initially thought they were massless, like photons. But experimentalists discovered that some neutrinos produced by the Sun “disappear” when they reach Earth; it turns out that the “missing” neutrinos have oscillated into other types of neutrinos. The oscillation phenomenon implies that neutrinos do have small masses. The non-zero neutrino mass is an indication of new physics beyond the standard model of particle physics. Oscillation experiments can measure the mass differences between different types of neutrinos, but we still don’t know the absolute mass scale of neutrinos nor why their masses are less than one-millionth the mass of an electron. Recent theories suggest neutrino mass is deeply connected to the dominance of matter in the universe.
To study neutrinos, we built state-of-the-art particle detectors deep underground, either in mines or tunnels inside tall mountains. The overburden in the underground locations shields the detectors from the harmful influence of high-energy cosmic rays. Using a combination of shielding techniques, we’ve created inside our experiments the most radio-quiet environment on Earth. The detectors themselves are constructed with specially chosen materials having ultra-low radioactive impurities.
My group plays a leadership role in the EXO-200 experiment, which utilizes enriched liquid xenon to study a very rare decay process, neutrinoless double beta decay. In this hypothetical process, two neutrons insides a nucleus decay into two protons with no emission of neutrinos. The discovery of this decay would signify that neutrinos are their own anti particles and illuminate the neutrino mass generation mechanisms. We are currently focused on developing new analysis techniques to perform the most sensitive searches with the EXO-200 data. We are also heavily involved in the R&D for the next-generation detector, nEXO, which promises to unravel the mystery surrounding the origin of the neutrino mass.
JESSIE SHELTON
I’m a theoretical particle physicist, and this is a really exciting, if puzzling, time to be working in the field. The cosmological history of our universe tells us unambiguously that there must be physics beyond what we currently understand. We have an enormous amount of evidence for some unknown form of dark matter from its gravitational pull on ordinary matter. Additionally, the cosmos shows a mysterious preference for matter over antimatter that ensures that we are all here today. These two observations mean that new particle physics has to be out there somewhere, but the real challenge right now is to figure out exactly where is the best place to look—we have very few hints from experiment as to what form any of this new physics should take.
One cornerstone of my current research is to come up with new ways to understand the footprints of dark matter in the cosmos. If dark matter happens to live off in its own shadow world, interacting with us (and our experiments) only rarely, these kinds of astrophysical footprints might be our best shot for unraveling the particle physics behind dark matter. I’m also very interested in making sure we take full advantage of the amazing discovery opportunities offered by the Large Hadron Collider. This is the only place in the world where Higgs bosons can be made, and we still have a lot to learn about this particle. The Higgs boson is one of our best windows into the kinds of shadow worlds where dark matter might live. I’ve thought a lot about what possible decays of the Higgs boson into shadow particles would look like—these would be rare, weird events, and a real challenge experimentally, but the insight they could offer into the Higgs boson, dark matter, and the structure of our universe would be profound.
ALEXEI AKSIMENTIEV
My group is using supercomputers to unravel the inner workings of biological cells and to design synthetic molecular machines that outperform their biological prototypes. Recent advances in biological sciences have provided a nearly complete list of biomolecules that make up a living cell. But how exactly that collection of molecules becomes a living being remains to be determined. Using computer models, my group is elucidating how biological phenomena originate from physical interactions between biomolecules. For example, we recently discovered that physical forces between DNA molecules depend on the genetic code they carry and can promote spatial segregation of DNA in a cell’s nucleolus, controlling which genes turn on and off.
Complementing theoretical studies of biological processes, my group is using computer simulations to advance applications of nanotechnology in medicine. In collaboration with experimental groups from around the world, we are developing nanopore readers of biological information, the nucleotide sequence of DNA and RNA and the amino-acid sequence of proteins, to be used in clinical diagnostics and basic research. We are exploiting the self-assembly properties of DNA to build synthetic analogs of biological nanomachines, such as membrane channels and rotary electromotors. Recently, we demonstrated a synthetic DNA nanostructure that flips lipids of a cell membrane thousands of times faster than any biological or synthetic system known to date.
VIRGINIA LORENZ
The ever-decreasing size of electronic components is leading to a fundamental change in the way computers operate. But at the few-nanometer scale, resistive heating and quantum mechanics prohibit efficient and stable operation. One of the most promising next-generation computing paradigms is spintronics, which uses the spin of the electron to manipulate and store information in the form of magnetic thin films. Although electron spin is a quantum-mechanical property, spintronics relies on macroscopic magnetization and thus does not take advantage of quantum mechanics in the algorithms used to encode and transmit information. Part of my group’s research focuses on optical studies of the fundamental mechanisms by which we can efficiently manipulate magnetization using electric current. We developed an optical magnetometer capable of sensitively measuring current-induced magnetization changes using a technique complementary to electrical measurement techniques. It allows us to study the magnetization changes that occur just a few nanometers beneath the surface of these materials.
My group also works on problems related to new computing and communication technologies based on the quantum mechanical properties of photons. Quantum technologies often require the carriers of information, or qubits, to have specific properties. Photonic quantum states are good information carriers because they travel fast and are robust to environmental fluctuations, but characterizing and controlling photonic sources so the photons have just the right properties is still a challenge. We are working to develop efficient techniques for determining the properties of the photonic quantum states as well as methods to control these properties. Examples include using stimulated emission, the basis of laser technologies, to enhance the signal-to-noise ratio of characterization measurements as well as developing devices to store and retrieve the information encoded in photons via material excitations, such as the excited states of atoms and solids.
GREG MACDOUGALL
My research group studies quantum materials and is dedicated to the discovery and exploration of exotic states of matter inside solids. In this branch of condensed matter physics, we study emergent phenomena in many-body systems—the amazing collective behavior of large numbers of particles working together that make these systems more than the sum of their parts. Illinois Physics has long been a world leader in this field, with an impressive level of expertise across a wide range of experimental and theoretical techniques held by talented researchers, working together inside a uniquely collaborative culture. My contribution is an expertise in the technique of neutron scattering.
Additionally, I maintain two laboratories at Illinois dedicated to materials discovery and crystal growth. Using our knowledge of the periodic table of elements and a toolbox of chemistry and crystal-growing techniques, we work to modify the properties of existing materials or to create entirely new materials, in a way that encourages unconventional behaviors. This includes materials that exhibit novel forms of superconductivity, interesting topological behaviors, and exotic forms of magnetism. One example is our recent discovery of material containing a so-called “spin-ice” state, wherein spins freeze into a non-equilibrium configuration with excitations that look like magnetic monopoles, but with additional evidence for strong quantum fluctuations. These properties raise the possibility at lower temperatures of a “quantum spin liquid” phase containing a long-ranged entanglement between magnetic moments. Another example is our work on manganese ferrimagnets, where we have seen that strong coupling between electron spins and atom positions allows us to create a state that self-separates into ordered and disordered regions separated by “domain walls,” which themselves order on the microscale and can be moved around with applied magnetic fields. A third example is our work on high-temperature copper-oxide superconductors, wherein quasi-1D spin and charge orders coexist with a spatially modulated “pair density wave” superconducting condensate having unique properties. The novelty of these states is such that a complete understanding often requires exploration with a variety of different experimental techniques and frequent consultation with theorists. In light of this, my group often collaborates with our condensed matter colleagues in the department and makes great use of local facilities housed in the Fredrick Seitz Materials Research Laboratory. My group is a prolific user of scattering instrumentation housed at national laboratories: most regularly, the neutron scattering instruments at the Spallation Neutron Source and High Flux Isotope Reactor at Oak Ridge National Laboratory, but also x-ray scattering facilities at Argonne National Laboratory and the Cornell High Energy Synchrotron Source and muon spin rotation spectrometers at the TRIUMF meson facility. In all cases, the ultimate goal of our research is not to understand the workings of any particular compound, but instead to illuminate the origin of novel and potentially useful behaviors that may extend to entire classes of materials.
My group also works on problems related to new computing and communication technologies based on the quantum mechanical properties of photons. Quantum technologies often require the carriers of information, or qubits, to have specific properties. Photonic quantum states are good information carriers because they travel fast and are robust to environmental fluctuations, but characterizing and controlling photonic sources so the photons have just the right properties is still a challenge. We are working to develop efficient techniques for determining the properties of the photonic quantum states as well as methods to control these properties. Examples include using stimulated emission, the basis of laser technologies, to enhance the signal-to-noise ratio of characterization measurements as well as developing devices to store and retrieve the information encoded in photons via material excitations, such as the excited states of atoms and solids.